The word "Chronic" means "long lasting", or "occurring over an extended period of time". A chronic illness one that you will have for a long time (if not for your entire life), or take a long time to recover from. A short-lived, sharp/intense/severe illness would instead be referred to (in formal language) as "Acute"
However, in informal usage, "Chronic" is frequently used to mean "severe" - such as a sudden painful migraine being referred to as a "chronic headache" even when relatively short-lived.
The word is also used in informal British English to mean 'bad, intense, severe, objectionable'
"Fowler's Dictionary of Modern English Usage" (1926) Henry Watson Fowler. Edited by Jeremy Butterfield in 2015
Certainly in Medical circles, you would never expect to see "Chronic" used in this way, even though it is a "new definition" for the word. However, someone recently asserted thusly to me (regarding the definition of a different word):
"There has to be some period of time after which the new lexical definition of a word can be accepted"
There are several questions this raises (I'm sure that Law.SE could find examples of when this would "invalidate" various Legal documents or rulings!), but the main one I was wondering is this:
What is the first record we have of "Chronic" being used in place of "Acute", its antonym?
There are other word-pairs in a similar situation, such as "Literally"/"Metaphorically", but this seemed an example with significant impact if the colloquial usage were to replace the official one