[countableC]T a small wheel, with teeth on its outeredge, that fits into a larger wheel and turns it or is turned by it 小齿轮
Examples from the Corpus
pinion• The upperdeckwindows could also be opened and closed together, with a rack and piniondevice.• A hydraulically powered rack and pinion swings the machine through 210°.• It held its wings like two hugeblackflags - only the great pinionsfluttered slightly.• Does anybody make pinions which I can use to put into the transferbox to replace the existing ones?• The old pinions used to hurt the old fellows so.• With his good hand Rhayader spread one of its immense white pinions.