Lacking way to get square (3,2,7)

I believe the answer is:

out of fashion

'square' is the definition.
(square can mean unfashionable)

'lacking way' is the wordplay.
'lacking' becomes 'out of' (to be out of something is to lack it).
'way' becomes 'fashion' (synonyms).
'outof'+'fashion'='OUT-OF-FASHION'

'to get' acts as a link.

(Another definition for out of fashion that I've seen is " Passe".)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.