Kami may, at its root, simply mean 'spirit', or an aspect of spirituality. It is written with the kanji "神", Sino-Japanese reading shin or jin; in Chinese, the character is used to refer to various nature spirits of traditional Chinese religion, but not to the Taoist deities or the Supreme Being. An apparently cognate form, perhaps a loanword, occurs in the Ainu language as kamui and refers to an animistic concept very similar to Japanese kami. In his translation of the Kojiki, Basil Hall Chamberlain provides the alternative interpretation that "The proper meaning of the word 'kami' is 'top', or 'above', and it is still constantly so used," citing the use of the word (short for ) to refer to the hair that grows from the top of the head, the use of the term "O Kami" to refer to governmental figures and otherwise societal superiors, and a provincial title which seems to have been used into the late 19th century.
Because Japanese does not normally distinguish singular and plural in nouns, it is sometimes unclear whether kami refers to a single or multiple entities. When a plural concept is absolutely necessary, the term is used. It is often said that there are —in Japanese the number "eight million" is often used to imply infinity.
Similarly, gender is also not implied in the word kami, which can be used to refer to either male or female kami. The word , meaning female kami is a relatively recent addition to the language, and is rarely, if ever used in traditional sources.
Some of the objects or phenomena designated as kami are qualities of growth, fertility, and production; natural phenomena like wind and thunder; natural objects like the sun, mountains, rivers, trees, and rocks; some animals; and ancestral spirits. Included within the designation of ancestral spirits are spirits of the ancestors of the Imperial House of Japan, but also ancestors of noble families as well as the spirits of the ancestors of common people.
There are other spirits designated as kami as well. For example, the guardian spirits of the land, occupations, and skills; spirits of Japanese heroes, men of outstanding deeds or virtues, and those who have contributed to civilization, culture and human welfare; those who have died for the state or the community (See: Yasukuni Shrine); and the pitiable dead. Not only spirits superior to man can be considered kami, but also spirits that are considered pitiable or weak have been considered kami in Shinto.
The concept of kami has been changed and refined since ancient times, although anything that was considered to be kami by ancient people will still be considered kami in "modern" Shinto. ("Modern" meaning since it was formalized into a unified religion under the influence of foreign religions like Buddhism.) Even within modern Shinto, there are no clearly defined criteria for what should or should not be worshipped as kami. The difference between modern Shinto and the ancient animistic religions is mainly a refinement of the kami-concept, rather than a difference in definitions.
In the ancient animistic religions, kami were understood as simply the divine forces of nature. Worshippers in ancient Japan revered creations of nature which exhibited a particular beauty and power such as waterfalls, mountains, boulders, animals, trees, grasses and even rice paddies. They strongly believed the spirits or resident kami deserved respect.
Although the ancient designations are still adhered to, in modern Shinto many priests also consider kami to be anthropomorphic spirits, with nobility and authority. These include such mythological figures as Amaterasu, the sun goddess of the Shinto pantheon. Although these kami can be considered deities, they are not considered omnipotent or omniscient. In the myths of Amaterasu, for example, she could not see the events of the human world. She also had to use divination rituals to see the future.
The kami traditionally possessed two souls, one gentle (nigi-mitama) and the other aggressive (ara-mitama). This human but powerful form of kami was also divided into amatsu-kami ("the heavenly deities") and kunitsu-kami ("the gods of the earthly realm"). A deity would behave differently according to which soul was in control at a given time. In many ways, this was representative of nature's sudden changes and would explain why there were kami for every meteorological event: snowfall, rain, typhoons, floods, lightning and volcanoes.
The ancestors of a particular family can also be worshipped as kami. In this sense, these kami were worshipped not because of their godly powers, but because of a distinct quality or value. These kami were regional and many shrines (hokora) were built in honour of these kami. In many cases, people who once lived can thus be deified as gods; an example of this is Tenjin, who was Sugawara no Michizane (845-903) in life.
In his 1946 Ningen-sengen radio broadcast, the emperor Hirohito declared that he is not an akitsumikami (manifest kami). However, after this declaration, Hirohito asked for permission from the occupying forces to worship his ancestors, and, upon receiving permission, he worshipped Amaterasu, thus implying that he was of divine descent.