observe
/əb-ˈzərv/
verb
to conform one's action or practice to (something, such as a law, rite, or condition) : comply, with
to inspect or take note of as an augury, omen, or presage
to celebrate or solemnize (something, such as a ceremony or festival) in a customary or accepted way
failed to observe the law and as a consequence had to pay a fine
idiom
to behave with politeness
We have never really liked each other, but we observe the social amenities whenever we meet.