synchromesh

n [U] device in a vehicle's gearbox that makes the parts turn at the same speed and thus allows gears to be changed smoothly （机动车齿轮箱中的）同步齿轮系.

symmetric, symmetrical, symmetrically, symmetry, sympathetic, sympathetically, sympathise, sympathize, sympathize with, sympathize, sympathise, sympathizer, sympathiser, sympathy, symphonic, symphony, symposium, symptom, symptomatic, synagogue, synapse, sync (also synch), synchronization, synchronisation, synchronize, synchronize, synchronise, synchronous, syncopate, syncopation, syncope, syndicalism, syndicalist, syndicate, syndication, syndrome, synergic, synod, synonym, synonymous, synopsis, synoptic, syntactic, syntactical,