It's smart of Charlie to put the pressure on (6)
I believe the answer is:
clever
'it's smart' is the definition.
(similar in meaning)
'charlie to put the pressure on' is the wordplay.
I cannot quite understand how this works, but
'charlie' could be 'c' (phonetic alphabet) and 'c' is located in the answer.
The remaining letters 'lever' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'of' acts as a link.
Can you help me to learn more?
(Other definitions for clever that I've seen before include "Bright; smart" , "brilliant" , "& 18 Down Smart Alec" , "Deft, able, bright" , "Mentally or physically skilful" .)