Woman taken aback, coming across Tory leader’s four-letter word (9)
I believe the answer is:
tetragram
'four-letter word' is the definition.
(I've seen this before)
'woman taken aback coming across tory leader's' is the wordplay.
'woman' becomes 'Margaret' (woman's name).
'taken aback' says the letters should be written backwards.
'coming across' indicates putting letters inside.
'tory leader's' becomes 't' (I've seen this in other clues).
'margaret' reversed gives 'teragram'.
'teragram' enclosing 't' is 'TETRAGRAM'.
(Other definitions for tetragram that I've seen before include "Say damn (but not blast)" , "familiar to geometricians !" , "Four-letter word" .)