Tmesis of prefixed verbs (whereby the prefix is separated from the simple verb) was an original feature of the Ancient Greek language, common in Homer (and later poetry), but not used in Attic prose. Such separable verbs are also part of the normal grammatical usage of some modern languages, such as German.
Tmesis is found as a poetic or rhetorical device in classical Latin poetry, such as Ovid's Metamorphoses. Words such as circumdare, to surround, are split apart with other words of the sentence in between, e.g. circum virum dant: "they surround the man". This device is used in this way to create a visual image of surrounding the man by means of the words on the line.
Tmesis in Ancient Greek is somewhat of a misnomer, since there is not necessarily a splitting of the prefix from the verb; rather the consensus now seems to be that the separate prefix or pre-verb reflects a stage in the language where the prefix had not yet joined on to the verb. There are many examples in Homer's epics, the Iliad and the Odyssey, both of which preserve archaic features. One common and oft-cited example is κατὰ δάκρυα λείβων kata dakrua leibōn "shedding tears", in which the pre-verb κατά kata "down" has not yet joined the verbal participle λείβων leibōn "shedding". In later Greek, these would combine to form the compound verb καταλείβων kataleibōn "shedding (in a downwards direction)".
One kind of tmesis involves the insertion of a word or phrase into another word, often for humorous effect. The insertion may occur between the parts of a compound word, or between syllable boundaries (dystmesis).
It is also referred to as tumbarumba, possibly due to the popularity of tmesis in Australian speech (Tumbarumba being an Australian town), or possibly due to the poem "Tumba Bloody Rumba" by John O'Grady, which includes several tmeses including "Tumba-bloody-rumba", "e-bloody-nough", and "kanga-bloody-roos".
Linguists sometimes describe tmesis as a form of infixation.
Representative English examples include: