Further letters after one or two from female or male relative (5)
I believe the answer is:
other
'further' is the definition.
(synonyms)
'letters after one or two from female or male relative' is the wordplay.
I cannot really understand how this works, but
'one' could be 'the' (both can introduce a definite example of something) and 'the' is located in the answer.
'or' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for other that I've seen before include "Different; additional" , "Very unusual" , "One may be significant" , "not like you" , "Alternative of two" .)