Hyperbole

Hyperbole is deliberate exaggeration used for emphasis or effect, stated in terms nobody is expected to take literally — 'the form had been on his desk since the Bronze Age'.

The form had been on his desk since the Bronze Age. Nobody believes it, and nobody is meant to. The exaggeration communicates an attitude — exasperation — faster and more precisely than any accurate statement of the delay.

That is the key point about hyperbole in fiction: it is almost never about the fact. It is about the speaker. A character who exaggerates is revealing what they find unbearable, and how much they expect to be indulged. Two narrators describing the same eight-month wait, one flatly and one hyperbolically, are two different people.

Its opposite number is litotes, which understates instead, and the two are often found in the same voice — extravagance about small things and dryness about large ones is a recognisable and very English comic register.

Hyperbole also shades into irony whenever the gap between the claim and the truth is wide enough that the gap itself is the message.

The failure mode is inflation. Hyperbole works by contrast with a plain surrounding register, so prose in which everything is the worst, the loudest, the most appalling has nowhere left to go when something genuinely large happens. Keep the baseline flat and the exaggeration will do its work. That is the same economy that governs purple prose.