Untimely means happening earlier than it should have. An untimely death, an untimely intervention, untimely frost.
Untimely death is by far the commonest use and is a formal way of saying somebody died young. Applied to a remark or an arrival it means badly timed rather than early. Note the older sense of untimely as unseasonable, of weather; and that timely means well-timed rather than early, so untimely is not quite its opposite — which is a small oddity of the pair.
1adjectiveuntimelyHappening earlier than it should have.
“The singer's untimely death at the age of twenty-seven shocked his fans.”
2adjectivebadlyBadly timed.
“Her untimely phone call woke the whole house at dawn.”
untimely is a quality of bad timing.
Middle English untymely is un- plus timely, and Old English had untidlic, meaning unseasonable, built the same way from tid, time.
Middle English
untymely
English, today
untimely
From Middle English untymely (also earlier untimliche), equivalent to un + timely. early 13th century. Compare Middle Danish utimelig, Old English untídlic (“unseasonable”).
Etymology from Wiktionary, CC BY-SA