croissant

Croissant comes from French croissant, the present participle of croître ("to grow"), which traces back through Old French creissant/croisant to Latin crēscō and ultimately to the Proto-Indo-European root *ḱer-.

In French, croissant simply meant "growing" or "crescent," describing a shape rather than a food; English borrowed the word whole, unadapted, letting it stand for the pastry itself.

It's a doublet of English crescent — both descend from the same Latin verb crēscō, one arriving through Old French sound changes, the other through French borrowed directly.