It's smart to join Charlie at the bar (6)
I believe the answer is:
clever
'it's smart' is the definition.
(similar in meaning)
'join charlie at the bar' is the wordplay.
I cannot quite understand how this works, but
'charlie' could be 'c' (phonetic alphabet) and 'c' is present in the answer.
'bar' could be 'lever' (lever is a kind of bar) and 'lever' is found within the answer.
No letters remain.
This explanation may well be incorrect...
'to' acts as a link.
Can you help me to learn more?
(Other definitions for clever that I've seen before include "Highly intelligent" , "& 18 Down Smart Alec" , "Quick-minded" , "Quick at learning, talented" , "Cute" .)