Androgynous French number is on old flame (6)
I believe the answer is:
unisex
'androgynous' is the definition.
(similar in meaning)
'french number is on old flame' is the wordplay.
'french number' becomes 'un' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'on' says to put letters next to each other.
'old flame' becomes 'ex' (an ex-lover).
'un'+'is'+'ex'='UNISEX'
Can you help me to learn more?
(Other definitions for unisex that I've seen before include "like St Hilda's now, > but not St Trinian's!" , "Available to men and women, clothes or hairdressing salons" , "Suitable for male and female" , "for boys and girls" , "Of clothing, hairstyles etc - suitable for men and women" .)