What to change when baby's sleepy? (5)
I believe the answer is:
nappy
'sleepy?' is the definition.
Both the answer and definition are adjectives. Maybe you can see an association between them that I don't see?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for nappy that I've seen before include "Baby garment" , "One pinned on baby" , "Baby's garment" , "Pad for baby" , "Baseball fielder" .)