furnace:  Etymologically, furnace means roughly ‘warm place’. It comes via Old French fornais from Latin fornāx ‘furnace’. This was a derivative of fornus ‘oven’, a word related to formus ‘warm’, which goes back to the same Indo-European source, *ghworm-, *ghwerm-, as probably produced English warm. => fornication
early 13c., from Old French fornais "oven, furnace," figuratively "flame of love" (12c.), from Latin fornacem (nominative fornax) "an oven, kiln," related to fornus/furnus "oven," and to formus "warm," from PIE root *gwher- "warm" (cognates: Greek thermos, Old English wearm; see warm (adj.)).
1. The flame in the furnace can be looked at through coloured glasses.
2. The furnace broke down and the entire office building has no heat.