Flaming sailor must be idle! (6)
I believe the answer is:
ablaze
'flaming' is the definition.
(synonyms)
'sailor must be idle' is the wordplay.
I cannot quite see how this works, but
'sailor' could be 'ab' (abbreviation for able seaman) and 'ab' is located in the answer.
'idle' could be 'laze' (synonyms) and 'laze' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for ablaze that I've seen before include "Fiery" , "Burning fiercely" , "being toasted?" , "Bright" , "On fire, burning" .)