Ruffian, working for university, is one showing a lot of cheek? (5)
I believe the answer is:
thong
'one showing a lot of cheek?' is the definition.
(skimpy undergarment)
'ruffian working for university' is the wordplay.
I cannot quite see how this works, but
'working' could be 'on' (e.g. a machine is working or on) and 'on' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
'is' is the link.
Can you help me to learn more?
(Other definitions for thong that I've seen before include "scanty garment" , "Strap - strip" , "Skimpy undergarment" , "Lash of whip" , "Leather whiplash" .)