Crossword Genius

When models that have lost their shape are employed? (6)

Ross

I believe the answer is:

seldom

I'm a little stuck... Click here to teach me more about this clue!

'when' is the definition.
Both the definition and answer are adverbs. Perhaps there's an association between them I don't understand?

'models that have lost their shape are employed?' is the wordplay.
'models' anagrams to 'SELDOM'.
But, I am not sure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for seldom that I've seen before include "Once in a blue moon" , "Not often, infrequently" , "Models (anag)" , "Only occasionally" , "Not 21" .)

I've seen this clue in The Globe and Mail.
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