Sack of bricks holding tons (3,2)
I believe the answer is:
let go
'sack' is the definition.
(thesaurus)
'bricks holding tons' is the wordplay.
'bricks' becomes 'lego' (I have seen 'Small bricks' mean 'lego' so perhaps 'bricks' could also mean 'lego').
'holding' means one lot of letters goes inside another.
'tons' becomes 't'.
'lego' enclosing 't' is 'LET GO'.
'of' is the link.
(Other definitions for let go that I've seen before include "Relax grip and release" , "Dismiss (from ones thoughts?)" , "Relinquish one's grip" , "Drop" , "Loose one's grip" .)