Barman's mass of ice (4)
I believe the answer is:
berg
This clue could be a double definition.
'barman's mass' is the first definition.
'berg' can be an answer for 'mass' (I have seen 'mass of ice' mean 'berg' so perhaps 'mass' could also mean 'berg'). I'm unsure of the 'barman's' bit.
'ice' is the second definition.
(thesaurus)
'of' acts as a link.
Can you help me to learn more?
(Other definitions for berg that I've seen before include "Small version of ice mountain" , "Mountain (in German, South African)" , "Large mass of floating ice" , "trouble at sea" , "He composed" .)