Engineer holds one very big wheel (9)
I believe the answer is:
executive
'big wheel' is the definition.
'engineer holds one very' is the wordplay.
'engineer' becomes 'execute' (**).
'holds' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'very' becomes 'v' (abbreviation).
'i'+'v'='iv'
'execute' enclosing 'iv' is 'EXECUTIVE'.
(Other definitions for executive that I've seen before include "boss" , "Having the power to act" , "Person or group with management powers" , "Company director" , "Business" .)