pastime vs avocation

pastime and avocation both are nouns.

Word	Noun	Adjective	Verb	Adverb
pastime	Yes	No	No	No
avocation	Yes	No	No	No

As nouns, avocation is a hyponym of pastime; that is, avocation is a word with a more specific, narrower meaning than pastime:

pastime: a diversion that occupies one's time and thoughts (usually pleasantly)
avocation: an auxiliary activity

Other hyponyms of pastime include by-line, hobby, pursuit, sideline, spare-time activity.

pastime (noun)	avocation (noun)
a diversion that occupies one's time and thoughts (usually pleasantly)	an auxiliary activity