A grain found in oak (5)

I believe the answer is:

acorn

'in oak' is the definition.
(I know that acorn is part of oak)

'a grain' is the wordplay.
'grain' becomes 'corn' (corn is a kind of grain).
'a'+'corn'='ACORN'

'found' acts as a link.

(Other definitions for acorn that I've seen before include "fruit in a cup" , "Might source" , "Fruit of the oak tree" , "from which something bigger may develop" , "mast" .)

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

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