Attempted while terribly tired (5)
I believe the answer is:
tried
'attempted while' is the definition.
'tried' can be an answer for 'attempted' ('try' can be a synonym of 'attempt'). I am unsure of the 'while' bit.
'terribly tired' is the wordplay.
'terribly' indicates an anagram.
'tired' anagrammed gives 'TRIED'.
Can you help me to learn more?
(Other definitions for tried that I've seen before include "Had a crack" , "Endeavoured" , "Put to the test" , "Made an effort" , "Attempted" .)