Frank is clever, dropping second of internationals for United (9)
I believe the answer is:
ingenuous
'frank' is the definition.
(similar in meaning)
'clever dropping second of internationals for united' is the wordplay.
I cannot really see how this works, but
'second' could be 's' (common abbreviation) and 's' is located in the answer.
'of' could be 'o' and 'o' is found within the answer.
'united' could be 'u' (abbreviation) and 'u' is present in the answer.
The remaining letters 'ingenu' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
'is' acts as a link.
Can you help me to learn more?
(Other definitions for ingenuous that I've seen before include "Free from deception" , "Innocent, unsuspecting" , "Naive" , "Frank" , "lacking sophistication" .)