Yes-man always so pleasant (9)
I believe the answer is:
agreeable
'pleasant' is the definition.
(similar in meaning)
'yes-man always' is the wordplay.
I cannot quite see how this works, but
'man' could be 'ab' and 'ab' is found in the answer.
This explanation may well be incorrect...
'so' acts as a link.
Can you help me to learn more?
(Other definitions for agreeable that I've seen before include "sympathetic" , "delightful" , "In harmony; pleasant" , "Pleasant, acceptable" , "Willing - nice" .)