Mostly grumpy character in bar (8)
I believe the answer is:
crotchet
'mostly grumpy character in bar' is the definition.
I can't judge whether this defines the answer.
'mostly grumpy character in bar' is the wordplay.
'mostly grumpy' becomes 'crotch' (I can't explain this - if you can you should give a lot more credence to this answer).
'character in' indicates the central letters (I've seen 'characters in' mean this).
'bar' becomes 'veto' (I've seen this before).
The middle of 'veto' is 'et'.
'crotch'+'et'='CROTCHET'
Can you help me to learn more?
(Other definitions for crotchet that I've seen before include "Peacock's castle" , "perverse notion" , "One in bar" , "Fancy" , "A note in music equal to half a minim" .)