(tres) noun
1. A lock, curl, or ringlet of human hair, especially when abundant: applied also, figuratively, to adornment suggesting tresses.
2. plural The hair of a woman or girl, especially when worn loose. [<OF tresce <LL tricia; ult. origin uncertain]
—tress′y adjective

Used in feminine nouns corresponding to masculine nouns in –ter, –tor: a contracted form of –teress, –toress. Compare –ER¹, –ESS.