Young lady heads for gents, avoiding lines (3)
I believe the answer is:
gal
'young lady' is the definition.
(synonyms)
'heads for gents avoiding lines' is the wordplay.
'heads for' indicates taking the first letters.
The first letters of 'gents avoiding lines' is 'GAL'.
(Other definitions for gal that I've seen before include "miss" , "Lady" , "measure of acceleration?" , "Young woman (colloq.)" , "An American girl, cowboy vintage" .)