means A heavy, long-sleeved pullover or top, usually made of thick cotton fleece, designed to absorb perspiration during exercise but worn just about everywhere now.

from A plain compound of "sweat" and "shirt," coined in the early 20th century when the garment was invented as athletic gear — the point was literally to soak up sweat. "Sweat" descends from Old English "swāt," a word with deep Germanic roots and cousins across the Indo-European family; "shirt" comes from Old English "scyrte," related to "short" and to "skirt" (a Norse borrowing of the same root) — all once meaning a short cut garment.