Reluctant to be beheaded for swear word (4)
I believe the answer is:
oath
'swear word' is the definition.
(I've seen this in another clue)
'reluctant to be beheaded' is the wordplay.
'reluctant' becomes 'loath' (synonyms).
'to be beheaded' means to remove the first letter (the head of the word is removed).
'loath' with its initial letter removed is 'OATH'.
'for' acts as a link.
(Other definitions for oath that I've seen before include "blasphemy" , "Curse or solemn promise" , "Strong language" , "Commitment to tell the truth" , "Solemn vow" .)