Teacher sounds a bit surly (3)
I believe the answer is:
sir
'teacher' is the definition.
(way of addressing a male teacher)
'sounds a bit surly' is the wordplay.
'a bit' indicates taking the first letters (I've seen 'bit of' mean this).
'surly' becomes 'ir' (I can't explain this - if you can you should believe this answer much more).
The first letter of 'sounds' is 's'.
's'+'ir'='SIR'
Can you help me to learn more?
(Other definitions for sir that I've seen before include "Term of address for a gentleman" , "Polite term of address for a man" , "Male title of respect" , "Polite or formal address to male" , "Noble title of undesirable kind" .)