Boss missing start of Disney film (4)

I believe the answer is:

umbo

'boss' is the definition.
(the boss on a shield)

'missing start of disney film' is the wordplay.
'missing start of' means to remove the first letter.
'disney film' becomes 'dumbo'.
'dumbo' with its initial letter taken away is 'UMBO'.

(Another definition for umbo that I've seen is " Boss on a shield".)

I've seen this clue in The Times.

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