Needless to say “astray” when a female’s lost (2,6)
I believe the answer is:
of course
'needless to say' is the definition.
I don't understand the rest of the clue.
(Other definitions for of course that I've seen before include "Assuredly, without doubt" , "Definitely" , "Obviously!" , "About a series of lessons" , "Naturally, goes without saying" .)