Still including a singular poet (5)
I believe the answer is:
yeats
'poet' is the definition.
(Yeats is an example)
'still including a singular' is the wordplay.
'still' becomes 'yet' (synonyms).
'including' means one lot of letters goes inside another.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'yet' enclosing 'a' is 'yeat'.
'yeat'+'s'='YEATS'
(Other definitions for yeats that I've seen before include "Poet William Butler or painter Jack B" , "William Butler .. . . ., Nobel-winning poet" , "Irish poet (The Winding Stair)" , "Irish poet and dramatist, d. 1939" , "he wrote" .)