heat: [OE] From an etymological point of view, heat is simply ‘hotness’ – that is, the adjective hot with an abstract noun suffix added to it. But the addition took place a long time ago, in the prehistoric ancestor of Old English. The suffix *-īn ‘state, condition’ was tacked on to the adjective *khaitaz ‘hot’ to produce *khaitīn, which eventually became modern English heat. The verb heat is equally ancient, and was independently formed from *khiataz (het, as in ‘het up’, comes from a dialectal form of its past participle). => het, hot
