Words get muddled at end of day when tired (6)
I believe the answer is:
drowsy
'tired' is the definition.
(I've seen this before)
'words get muddled at end of day' is the wordplay.
I cannot quite see how this works, but
an anagram of 'words' is 'drows' which is present in the answer.
A single letter 'y' remains which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'when' acts as a link.
Can you help me to learn more?
(Other definitions for drowsy that I've seen before include "Dull" , "Almost asleep" , "Disinclined to stay awake" , "liable to drop off" , "Sleepy, half-asleep" .)