Change in middle of genuine weariness (5)
I believe the answer is:
ennui
'weariness' is the definition.
(ennui is weariness or boredom)
'change in middle of genuine' is the wordplay.
'change in' is an anagram indicator.
'middle of' means to look at the middle letters.
The centre of 'genuine' is 'enuin'.
'enuin' anagrammed gives 'ENNUI'.
(Other definitions for ennui that I've seen before include "to make one list less when connected" , "Lower interest rate" , "Boredom, tedium" , "Feeling of disaffection" , "French boredom and lassitude" .)