custom vs ritual

custom and ritual both are nouns.

Word	Noun	Adjective	Verb	Adverb
custom	Yes	Yes	No	No
ritual	Yes	Yes	No	No

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

Other hyponyms of custom include Americanism, Anglicism, Britishism, consuetude, couvade, Germanism, habit, use, hijab, rite.

custom (noun)	ritual (noun)
accepted or habitual practice	any customary observance or practice
habitual patronage	the prescribed procedure for conducting religious ceremonies
a specific practice of long standing	stereotyped behavior
money collected under a tariff

custom (adjective)	ritual (adjective)
made according to the specifications of an individual	of or relating to or employed in social rites or rituals
	of or relating to or characteristic of religious rituals