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flashpoint (US English - flash point)
noun

- a place or stage at which violence might be expected to begin

(Cambridge Advanced Learner's Dictionary)

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In the field of chemistry, flashpoint is the temperature at and above which a liquid gives off enough flammable vapour to form a mixture with air that can be ignited by contact with a hot surface, spark, or flame. With a low flashpoint, petrol is an ideal fuel for combustion engines for example. The downside is that it is more dangerous to handle since it's highly flammable.

Since the flashpoint for a particular chemical is somewhat unreliable, this gave rise to the figurative sense of a place, event, or time at which violence or hostility flares up. This usage first appears in the mid 1950s. The words flash and point are considerably older however.

Flash is from the 15th century and stems from "flasken," (and later flaschen), an Old English verb meaning to splash or dash water. This is likely imitative of the sound. The meaning of giving off a sudden short light or flame is not recorded until the mid 1500s.

Point is probably before the 1200s and is a merger of two words: a very small amount/single item in a whole and the sharp end of a sword. Both of these meanings are ultimately from the Latin "pungere," to "prick, pierce, puncture."

The Latin neuter present participle "punctum" was used as a noun, meaning "small hole made by pricking," and subsequently extended to anything that looked like one, hence, "dot, particle," etc. This yielded the Old French "point" - smallest amount - which was borrowed into Middle English by the 13th century.

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SYNONYMS

hot spot, powder keg, time bomb

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SMUGGLE OWAD into today's conversation

"Keep away from the south side of the city, it's a flashpoint for gang activity."