Courage, informally (4)
I believe the answer is:
guts
'courage informally' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for guts that I've seen before include "Courage (coll.)" , "Inside - bottle!" , "Cleans - bottle" , "Courage, determination" , "Fortitude - innards" .)