Shape that betrays a lack of freshness (5)

I believe the answer is:

mould

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

'shape' is the definition.
(moulding is a kind of shaping)

I can't explain the remainder of the clue.

(Other definitions for mould that I've seen before include "die?" , "Growth due to fungi" , "jelly?" , "Furry growth of minute fungi" , "Crumbly soil" .)

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

Want a hint initially instead of a full solution? Install my app