Back in the liner I spotted a fascinating female (5)
I believe the answer is:
siren
'female' is the definition.
(siren is a kind of female)
'back in the liner i spotted a fascinating' is the wordplay.
'back' is a reversal indicator.
'in' indicates a hidden word.
'neris' can be found hidden inside 'liner i spotted fascinating'.
'neris' reversed gives 'SIREN'.
(Other definitions for siren that I've seen before include "Warning sound" , "Bewitching singer,part- woman, part-bird" , "Nymph supposed to have lured sailors to destruction on rocks" , "Seductive woman" , "'Delilah!'" .)