Wiktionary(0.00 / 0 votes)Rate this definition: fume(Noun) A gas or vapour/vapor that smells strongly or is dangerous to inhale. Fumes are solid particles formed by condensation from the gaseous state, e.g. metal oxides from volatilized metals. They can flocculate and coalesce. Their particle size is between 0.1 and 1 micron.