Spectacles no good for girls (6)
I believe the answer is:
lasses
'girls' is the definition.
(lass is a kind of girl)
'spectacles no good' is the wordplay.
'spectacles' becomes 'glasses' ('glasses' can be a synonym of 'spectacles').
'no' suggests deleting specific letters.
'good' becomes 'g' (abbreviation).
'glasses' with 'g' taken away is 'LASSES'.
'for' is the link.
(Other definitions for lasses that I've seen before include "Young ladies" , "Northern girls?" , "Lads and - -" .)