When Did People Start Saying “Unthaw” to Mean “Thaw”?

Robin in Jacksonville, Florida, grew up using the word unthaw as in unthaw the frozen hamburger until someone told her that she should instead simply say thaw to mean “allow something frozen to come to room temperature.” Is it wrong to say unthaw? It’s less common and less formal than plain old thaw, but the word unthaw has been in use for at least four centuries. In the 1600s, the prefix un- was added as an emphasizer to several words, including the adjectives boundless, helpless, remorseless, and witless to form unboundless, unhelpful, unremorseless, and unwitless as a way of intensifying their meaning. Similarly, verbs such as ravel, peel, loosen can be rendered as unravel, unpeel, and unloosen. The point is that the prefix un- doesn’t always negate — sometimes it serves to emphasize. This is part of a complete episode.