Yearn to join senior member and poet (10)
I believe the answer is:
longfellow
'poet' is the definition.
(Henry Wadsworth Longfellow, 1807-1882)
'yearn to join senior member' is the wordplay.
'yearn' becomes 'long-' (synonyms).
'to join' means one lot of letters go next to another.
'senior member' becomes 'fellow' (I can't explain this - if you can you should believe this answer much more).
'long'+'fellow'='LONGFELLOW'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for longfellow that I've seen before include "Song of_Hiawatha poet" , "American poet, author of 17" , "Hiawatha poet" .)