apricity

The warmth of the sun in winter.

Here’s an amusing skit on such rare words, from Mirriam-Webster

“These humicubations, the nocturnal irrorations, and the dankishness of the atmosphere, generated by a want of apricity, were extremely febrifacient.” Lorenzo Altisonant (aka Samuel Klinefelter Hoshour), Letters to Squire Pedant, 1856