Meaning

noun a padded cloth covering to keep a teapot warm

adjective enjoying or affording comforting warmth and shelter especially in a small space

originFrom Scots cosie, from Old Scots colsie, but ultimate derivation is unknown. Possibly of North Germanic origin, such as Norwegian kose seg (“to have a cozy time”), from Old Norse kose sig, from koselig, koslig, perhaps ultimately from Old High German kōsa; see modern German kosen (“to cuddle”).

Etymology from Wiktionary, CC BY-SA 3.0