Words get muddled at day's end when tired (6)
I believe the answer is:
drowsy
'tired' is the definition.
(I've seen this before)
'words get muddled at day's end' 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 explanation may well be incorrect...
'when' is the link.
Can you help me to learn more?
(Other definitions for drowsy that I've seen before include "Almost asleep" , "Comatose" , "Wanting to nod off" , "liable to drop off" , "Sleepy, somnolent" .)