Suggestion bizarrely so popular, to leave university (8)
I believe the answer is:
proposal
'suggestion' is the definition.
(I've seen this before)
'bizarrely so popular to leave university' is the wordplay.
'bizarrely' is an anagram indicator.
'to leave' suggests deleting specific letters.
'university' becomes 'u'.
'so'+'popular'='sopopular'
'sopopular' with 'u' taken out is 'sopoplar'.
'sopoplar' anagrammed gives 'PROPOSAL'.
(Other definitions for proposal that I've seen before include "a match might be arranged?" , "union offer?" , "Kind of offer, perhaps of marriage" , "motion" , "Offer - suggestion" .)