flare-up

The word 'flare-up' is a nominalization of the phrasal verb 'to flare up'. The verb 'flare' itself has obscure origins, potentially linked to Old Norse or imitative roots suggesting unsteady light or motion. When combined with the adverbial particle 'up', common in Germanic languages to denote sudden onset or completion, it creates a vivid image of a fire or emotion bursting into sudden, noticeable activity. This literal sense of a fire blazing up was extended metaphorically to describe any sudden, intense outbreak, such as violence, illness, or anger, capturing the concept of a latent condition rapidly becoming active and visible.

Structure: flare (to burn) + up (completive particle) - flare: Of uncertain origin, possibly from Old Norse or Middle English, meaning to spread out, blaze, or burn unsteadily. In this compound, it functions as the core verb indicating a sudden, bright burning or outburst. - up: From Old English ūp, an adverb and particle. In phrasal verb constructions like 'flare up', it acts as a completive particle, often indicating suddenness, intensity, or public emergence.