On some days, sailors do their mending (4)
I believe the answer is:
darn
'mending' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'on some days sailors do' is the wordplay.
I cannot quite see how this works, but
'some' could be 'a' and 'a' is located in the answer.
'days' could be 'd' (abbreviation for days) and 'd' is present in the answer.
'sailors' could be 'rn' (abbreviation for Royal Navy) and 'rn' is found in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'their' acts as a link.
Can you help me to learn more?
(Other definitions for darn that I've seen before include "Mend (knitted material)" , "Repair by sewing, socks perhaps" , "Repair (with needle)" , "Mend with a needle" , "Stitch" .)