Make tea of calibre - weak (4)
I believe the answer is:
brew
'make tea' is the definition.
(I've seen this before)
'of calibre weak' is the wordplay.
'of' indicates the answer is hidden within the clue.
'BREW' is hidden in the letters of 'calibre weak'.
(Other definitions for brew that I've seen before include "Steep" , "Infusion" , "Make (tea/coffee)" , "A pot of tea?" , "Plot" .)