Contracted the blue film cast for small amount (10)

I believe the answer is:

thimbleful

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'small amount' is the definition.
'thimbleful' can be an answer for 'amount' (thimbleful is a kind of amount). I'm not certain of the 'small' bit.

'contracted the blue film cast' is the wordplay.
'contracted' becomes 'th' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'cast' indicates anagramming the letters.
'blue'+'film'='bluefilm'
'bluefilm' is an anagram of 'imbleful'.
'th'+'imbleful'='THIMBLEFUL'

'for' acts as a link.

Can you help me to learn more?

I've seen this clue in The Telegraph.

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