vuonna

Etymology
An old essive (originally locative) singular form of. Originally, essive forms with consonant stems went through a greater degree of assimilation (vuonna < *voonna < *vootna < *voote-na), but were later made more regular again by analogy.

Adverb

 * 1) in the year

Usage notes

 * is treated as if it were an essive form, so any determiner or adjective used with it will be inflected in the essive case as well (e.g. ). Nevertheless, also has a regular essive form, . This is also used in certain contexts.
 * In particular, is used in expressions when talking about a year during which something takes or took place, while the other, more general uses of the essive case (see appendix), including essive-governed verb phrases, are relegated to.
 * However, outside of specific uses (when followed by a numeral or preceded by one of a few common words), may be used in place of . There is no clear pattern for which form is used in these cases, and it often depends on the speaker.
 * The common words with which is practically always used include (but is not necessarily restricted to), , , ,  and.
 * A traditional rule states that can never take a possessive suffix, and thus in cases where one is needed,  must be used. However, in practice,  can be seen in many texts with a possessive suffix.