Fearless girl, leader in foreign incursion (8)
I believe the answer is:
unafraid
'fearless' is the definition.
(associated in meaning)
'girl leader in foreign incursion' is the wordplay.
'girl' becomes 'Una' (girl's name).
'leader in' says to take the initial letters.
'incursion' becomes 'raid' (raid is a kind of incursion).
The initial letter of 'foreign' is 'f'.
'una'+'f'+'raid'='UNAFRAID'
(Other definitions for unafraid that I've seen before include "Feeling no fear" , "Not timorous or apprehensive" , "not daunted" , "Not cowed" , "game" .)