Very insignificant thing featuring in terribly asinine film (13)

I believe the answer is:

infinitesimal

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'very insignificant' is the definition.
I can't judge whether this defines the answer.

'thing featuring in terribly asinine film' is the wordplay.
'thing' becomes 'it'.
'featuring in' means one lot of letters goes inside another.
'terribly' is an anagram indicator.
'asinine'+'film'='asininefilm'
'asininefilm' anagrammed gives 'infinesimal'.
'it' inserted within 'infinesimal' is 'INFINITESIMAL'.

Can you help me to learn more?

(Other definitions for infinitesimal that I've seen before include "Extremely small" , "Minute" , "Tiny" , "So small as to be barely discernible" , "Immeasurably small" .)

I've seen this clue in The Times.

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