Crossword Genius

Needless to say “astray” when a female’s lost (2,6)

Ross

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" .)

I've seen this clue in The Times.
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