One US institute worker's counterfeit (7)
I believe the answer is:
imitant
'counterfeit' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'one us institute worker's' is the wordplay.
'one' becomes 'i' (Roman numeral).
'us institute' becomes 'MIT' (Massachusetts Institute of Technology).
'worker' becomes 'ant' (worker is a type of ant).
'i'+'mit'+'ant'='IMITANT'
Can you help me to learn more?
(Another definition for imitant that I've seen is " copy".)