Crossword Genius

Some terrorist essentially caught by FBI at building (1,3,2)

Ross

I believe the answer is:

a bit of

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'some' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.

'terrorist essentially caught by fbi at building' is the wordplay.
'essentially' indicates the central letters.
'caught by' means one lot of letters goes inside another.
'building' is an anagram indicator.
The middle of 'terrorist' is 'o'.
'fbi'+'at'='fbiat'
'fbiat' anagrammed gives 'abitf'.
'o' placed inside 'abitf' is 'A BIT OF'.

Can you help me to learn more?

(Another definition for a bit of that I've seen is " somewhat".)

I've seen this clue in The Hindu.
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