to enter, go into, get into a place or a thing / to join a group or organization / to be contained (in), to be included (in) / to be a member of a group, set, category

polyamide

(Internet slang) dirty room

at-home clothes

an adult son residing with his parents; generally has not yet or can not come into family inheritance / a female servant working in a daimyō, ōoku, or other high-ranking house

room rent

(mechanics) aerodynamics

(exercise) wall squat / A group activity where a ring of people attempt to maintain the position of "sitting" on the lap of the person behind them.

air gun

(colloquial) unable to pick up on social cues or the situation; lacking social awareness or situational awareness