Contraction of insanity intermittently observed (4)
I believe the answer is:
isnt
'contraction' is the definition.
Both the answer and definition are singular nouns.
Maybe they are linked in a way I don't understand?
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for isnt that I've seen before include "Ain't" , "Tins (anag.)" , "Is not (abbrev.)" , "When abridged, has none of the quality of" , "Does not happen to be" .)