Crossword Genius

Thumb prodded into awkward person in government department (7)

Ross

I believe the answer is:

customs

I'm a little stuck... Click here to teach me more about this clue!

'thumb' is the definition.
Although both the answer and definition are singular nouns, I can't understand how one could define the other.

'prodded into awkward person in government department' is the wordplay.
I cannot quite understand how this works, but
'person' could be 'ms' (Ms. is an example) and 'ms' is found within the answer.
'government' could be 'us' (U.S. is an example) and 'us' is present in the answer.
The remaining letters 'cto' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for customs that I've seen before include "state's duties?" , "Traditions" , "Traditional ways" , "Port/airport department" , "Import duties" .)

I've seen this clue in The Guardian.
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