A woman in bed is unable to (6)
I believe the answer is:
cannot
'is unable to' is the definition.
(I've seen this before)
'a woman in bed' is the wordplay.
'a woman' becomes 'ann'.
'in' indicates putting letters inside.
'bed' becomes 'cot' (cot is a kind of bed).
'ann' going within 'cot' is 'CANNOT'.
(Other definitions for cannot that I've seen before include "Is unabe to" , "Defeatist's word?" , "Canton (anag.)" , "Is unable to" , "Is not in a position to" .)