Older linguistic manuals often emphasize the alleged significant influence Iranian languages have exerted on Proto-Slavic. Some contemporary Slavists, like Gołąb (1992), think that all Slavic words with unexplained initial *x- are in fact Iranianisms in Slavic. Matasović (2008) criticizes Gołąb's approach as "methodologically inacceptable, emphasizing that initial *x- in Slavic has several sources, some of which have been ascertained (like PIE *#ks-), and some of which have not been completely determined, and emphasizes that all the cases of initial *x- in Slavic should first be explained by means of regular Slavic sound laws, and only then should one think of loanwords, and think of Iranian as the originator if and only if the etymon has been attested in Iranian, and there is additional phonetic evidence to presume an Iranian borrowing.
In the past, various Slavists have emphasized how certain Iranianisms in Slavic are in fact surprisingly few. Vaillant and Meillet consider the only Iranian borrowings in Slavic word *taparu 'axe' (Russ. топор#Russian, Pol. topór#Polish. Cr. topor#Croatian), which came from Iranian *tapara- (cf. Persian تبر#Persian). This is how Meillet and Vaillant explain the lack of Iranianisms in Slavic:
That fact should not surprise us: the civilization of warrior and partially nomadic tribes, like Scythian and Sarmatian, could have exerted only a cursory influence on patriarchal civilization of Slavs.
But event they do not deny that there are traces of some influence of Iranian onto Slavic, such as in the semasiological development of the word god, which both in Slavic (Proto-Slavic *bagu > Common Slavic Appendix:Proto-Slavic *bogъ) and Indo-Iranian (Old Persian 𐎲𐎥#Old_Persian, Sanskrit भग#Sanskrit) denotes both deity and wealth, share.
Beside Gołąb (1992), Matasović (2008) says that the number of alleged Iranianisms compiled by Reczek (1885) and Bernštejn (1961-74) is "too high in number", and that out of the listings compiled by them one should separate words which are likely Iranian borrowings from words that are possibly Iranian borrowings, but have other possible explanations, by means of Proto-Indo-European, Proto-Balto-Slavic or Proto-Slavic derivation via regularly observed sound laws. Matasović states that "solving the problem of Iranian loanwords in Slavic, their distribution and relative chronology, is one of the most important tasks of modern Slavic studies.
Some of the likely Iranian borrowings are also Common Slavic, being attested in more than one branch. Such are:
Others have been attested only in a part of Slavic territory. E.g.
Matasović (2008) also notes on surprising typological coincidences between Slavic and Ossetian, Iranian language whose ancestor was Alanic. Ossetian, just like Slavic, divides verbs onto perfective and imperfective, and derives perfective verbs from imperfective by means of prefixation. Also, pronominal clitics in Ossetian behave syntactically similar to Slavic, and similar is the usage of genitive to express direct object in some constructs. It remains open, however, whether those correspondences are a result of prehistorical contacts of Slavic and Alanic tribes, or just a case of accidental typological parallelism in development.
Goths are the first Germanic people for which it can be proved to have intensive contacts with Proto-Slavs. Goths are believed to have reached the shores of the Black sea between Dniester and Danube about 230 C.E., so the contacts between Goths and Proto-Slavs might have started in the 2nd and the 3rd century C.E., and continue all the way to the early historical period.
It is belived that many terms of Greco-Roman cultural provenience have entered the Proto-Slavic by Gothic mediation. Such are the terms:
Here is a list of words which are generally held to be Germanic loanwords into Proto-Slavic:
As one can see, Germanic borrowings in Proto-Slavic cover diverse semantic fields, but consist mostly of words that are commonly borrowed in languages; terms related to: building (*xūzu, *mastu, *tūnu), land configuration (*xulmu. *bergu), terms from social domain (*pulku, *želdān, *kōpītej, *činda), apellations for animals and cattle (*asilu, *gansi, *skatu).
Gołąb (1992) suggests even more refined chronological layering, emphasizing that one should distinguish
Generally, all authors agree that Germanicisms have entered Proto-Slavic and Common Slavic during a very long period, and that numerous Slavic sound changes came be observed on them. For example, there are Germanic loanwords that have entered pre-Proto-Slavic, before the Slavic first palatalization (e.g. *činda, *želdān, *xelmu), or before the transition of PSl. *aw > PSl. */ō/ (e.g. *lōku, *kōsitej, *kōpitej).
Of special interests are certain Proto-Slavic accentual developments that can be observed on Germanic borrowings:
Germanic loanwords have entered Slavic languages well after the Proto-Slavic, i.e. in Common Slavic period. After the 600 C.E. most of them were borrowed from Old High German, and for some of them they can even be proved to be of OHG and not e.g. Gothic origin.
Among Slavicisms in Germanic prominent are the words related to crafts and social sphere:
These words don't tell much about phonological history of Proto-Slavic, but it's obvious that they were borrowed before liquid metathesis, but after the Proto-Slavic change *pt > *t.
It should be noted that some linguists consider the existence of Slavic borrowings into Germanic very doubtful.
However, since in pre-historical times Celts populated the regions in which Slavs have spread in the 6th and the 7th century, one cannot exclude the possibility that at the time of Slavic expansion there were some some Celtic speakers left. Matasović (2008) also emphasizes the very likely possibility of Celtic borrowings that might have entered Slavic but mediated by Vulgar Latin/early Romance dialects, since such marginally spoken Celtic was probably non-prestigious idiom spoken by lower class of society. Concordingly, Matasović argues, any possible Celtic borrowings into Slavic must come from earlier period, i.e. they had to be borrowed in pre-Proto-Slavic from Proto-Celtic.
Many Slavic words of obscure etymologies have been explained in literature as some alleged Celtic borrowings, but only for only a few of them can that claim be substantiated by linguistic evidence, one that agrees with attested etymons semantically and by regular sound laws. Matasović (2008) lists 2 examples as highly probable:
Matasović (2008) argues however:
Non of these theses can be held as proved, until we can point to a stratum of words which reflect, judging from their phonetic/phonological traits, Italic, Venetic or Armenian mediation between Proto-Indo-European and Proto-Slavic. This means that, in order to accept the existence of Italic loanwords into Proto-Slavic, we must be able to prove the operation of Italic sound laws on the set of Proto-Slavic etymons.
In practice, however, Slavic etymons with obscure etymologies have not so rarely been ascribed to such sources, with ad-hoc devised sound changes and far-fetched semantic correlation. Sometimes they often represent regular Proto-Indo-European reflexes, but have only been preserved in e.g. Slavic in Italic branch, which has falsely led to the conclusion that they represent a prehistorical borrowing.
Beside the contacts with other Indo-European languages, there is undoubtedly a layer of word that were borrowed from non-Indo-European languages. Most of these came from Turkic languages, chiefly Bulgar and Eurasian Avar. For most of them, it's very hard to establish the exact source and reconstruct the proto-form. Among these, commonly cited are: