Crossword Genius

Shop ineffectively as stated every fortnight (8)

Ross

I believe the answer is:

biweekly

'every fortnight' is the definition.
(biweekly can mean happening every fortnight)

I cannot understand how the remainder of the clue works.

(Other definitions for biweekly that I've seen before include "(Of a publication) 26 issues per year" , "once a fortnight" .)

I've seen this clue in The Times.
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.