Chivalrous Liberal worker supporting young woman (7)
'chivalrous' is the definition.
('gallant' can be a synonym of 'chivalrous')
'liberal worker supporting young woman' is the wordplay.
'liberal' becomes 'l' (abbreviation).
'worker' becomes 'ant' (worker is a type of ant).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'young woman' becomes 'gal' ('gal' can be a synonym of 'young woman').
'lant' put after 'gal' is 'GALLANT'.
(Other definitions for gallant that I've seen before include "Dashing gentleman", "lady-killer?", "Bold", "Brave and chivalrous like knight of old", "Valiant; courteous".)