Plump guide sadly exhausted (8)
I believe the answer is:
fatigued
'exhausted' is the definition.
('fatigued' can be a synonym of 'exhausted')
'plump guide sadly' is the wordplay.
'plump' becomes 'fat' ('fat' can be a synonym of 'plump').
'sadly' indicates an anagram.
'guide' is an anagram of 'igued'.
'fat'+'igued'='FATIGUED'
(Other definitions for fatigued that I've seen before include "Drained of energy" , "needing the rest" , "Tired, really weary" , "Exhausted" , "Extremely tired" .)