flamma

Flamma, flammae, f., is first declension. Against ignis, which is fire as substance or element, flamma is the visible tongue of it, the blaze you can point at. That distinction survives in the idioms: ferro et flamma, "with sword and fire", is what an army does to a district.

The metaphor is fixed and unembarrassed. Flamma amoris is the standard image, and in the elegists flamma on its own means passion with no further explanation needed. The bride veil was the flammeum, flame-coloured, and the priest of Jupiter was the flamen. English has flame through Old French, plus inflame, flammable and, by a Latin mistake nobody has fixed, inflammable meaning the same thing rather than the opposite.