(idiomatic) To attend a class, educational presentation, meeting, etc. for one time, as a visitor. / (music) To take part in a group musical performance, especially a jazz session, as a temporary guest.

The operating of a new engine (especially that of a motor vehicle) at less than its normal speed until proper working has been established.

plural of pain in the ass

present participle of hand in

Third-person singular simple present indicative form of hand in

simple past tense and past participle of hand in

Third-person singular simple present indicative form of give in

present participle of give in

A substitute; a replacement.

To substitute for; to replace; (theater) to serve as an understudy. / To make one of a party in a bet or other speculation. / To take a side in a dispute.