Single woman's first in cubicle block (9)
I believe the answer is:
stonewall
'block' is the definition.
(I know that block is a is a kind of of stonewall)
'single woman's first in cubicle' is the wordplay.
'single' becomes 'one' (a single thing - only one).
'woman's first' becomes 'w' (1st letter of 'woman').
'in' is an insertion indicator.
'cubicle' becomes 'stall' (synonyms).
'one'+'w'='onew'
'onew' inserted into 'stall' is 'STONEWALL'.
(Other definitions for stonewall that I've seen before include "Play to defend" , "Engage in delaying tactics - General Jackson?" , "Refuse to co-operate" , "Delay or block (a proposal's) progress" , "Stand firm" .)