A profession, a job for which one is qualified or suited, a calling.
Usage: It isn't often that a word is separated from its antonym by a single letter, but a job one does after work and not for salary—a hobby, is an "avocation." Moreover, take that [a] and write it over the [o] and we get "vacation," which is time taken off from one's vocation (and unrelated to "vocation").
The adjective for today's word is "vocational" and the adverb, "vocationally."
Suggested Usage: "Avocation" has been confused with "vocation" for centuries now, so that most dictionaries currently list the two as synonyms. That doesn't mean we should not distinguish them in careful speech: "Thomasina's vocation is cleaning the homes of others and her avocation is cleaning her own." Here is another way to distinguish these two similar words: "Fuzzy Witt was so successful at his avocation, painting rocks and selling them as pets, that he decided to make it his vocation."