Defence work to have second thoughts about? (7)
I believe the answer is:
redoubt
'defence' is the definition.
(I know that redoubt is a type of fortification)
'work to have second thoughts about?' is the wordplay.
I cannot quite see how this works, but
'work' could be 'do' (synonyms) and 'do' is found in the answer.
'second' could be 're' (prefix meaning second in eg review, re-education) and 're' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for redoubt that I've seen before include "Obtrude in kind of military fieldwork" , "temporary defence work" , "Keep losing confidence in" , "Temporary military fortification" , "In final retreat" .)