Poem causing wild glee at the end of the day (5)
I believe the answer is:
elegy
'poem' is the definition.
(I know that elegy is a type of poem)
'wild glee at the end of the day' is the wordplay.
'wild' indicates anagramming the letters.
'at the end of' says to take the final letters.
The final letter of 'day' is 'y'.
'glee' is an anagram of 'eleg'.
'eleg'+'y'='ELEGY'
'causing' is the link.
(Other definitions for elegy that I've seen before include "Mournful song or poem" , "Sad words" , "Poem of mourning" , "Poem penned beside church" , "Work of poet" .)