means Having or giving off a moderate, pleasant heat — or, of a person or feeling, showing affection and friendliness.

from From Old English 'wearm,' tracing back to a Proto-Germanic root (a cousin of German 'warm' and Dutch 'warm') and ultimately a Proto-Indo-European source that may be related to words for both warmth and burning — possibly the same ancient root that gives us 'thermal' through Greek. So the cozy and the scorching have likely shared a hearth for a very long time.