Learned book about backward female pair (7)
I believe the answer is:
twosome
'pair' is the definition.
(I know that twosome is a type of pair)
'learned book about backward female' is the wordplay.
'learned book' becomes 'tome' (I've seen this in another clue).
'about' means one lot of letters goes inside another.
'backward' shows that the letters should be reversed in order.
'female' becomes 'sow' (female pig).
'sow' in reverse letter order is 'wos'.
'tome' going around 'wos' is 'TWOSOME'.
(Other definitions for twosome that I've seen before include "Couple" , "game of golf" , "Pair, duo" , "Item" , "match" .)