Chronic describes something that goes on and on and will not clear up. Back pain that has lasted nine years, a cough every winter since childhood, a knee that never fully came back.
The word is about time, not severity, and that is the mistake to avoid: chronic is the opposite of acute, not of mild. An acute illness comes on fast and ends; a chronic one settles in and stays, however gentle it is. Outside medicine it fastens onto long-running problems — a chronic shortage of nurses, chronic underfunding, chronic delays — and it never attaches to good things, so there is no chronic happiness. British speech has an old slang use where chronic simply means terrible, as in the weather was chronic, and it sounds dated now. The adverb does the same work: chronically ill, chronically late.
1adjectivechronicLasting a long time and not going away — said of an illness, a pain or a condition.
“She has managed chronic pain since the accident.”
2adjectivepersistentGoing on for years with no sign of ending — said of a bad situation.
“The hospital has a chronic shortage of beds.”
synonyms: persistent, long-standing, entrenched
3adjectiveindeedVery bad indeed — dated British slang.
“The service in that place is chronic.”
Chronic came through Latin chronicus from Ancient Greek khronikos, 'of time', built on khronos, time. That is the whole word: time-ish. Its relatives keep the clock too — chronicle, chronology, chronometer — and a chronic illness is named for how long it lasts, not for how much it hurts.
Ancient Greek
χρονικός — of time
Latin
chronicus
Old French
cronike
English, today
chronic
Built from
From chronical, from Old French cronike, from Latin chronicus, from Ancient Greek χρονικός (“of time”), from χρόνος (“time”). by surface analysis, chron- + -ic.
Etymology from Wiktionary, CC BY-SA