Animal shelter reported infection (4)
I believe the answer is:
stye
'animal shelter' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'reported infection' is the wordplay.
'reported' indicates a 'sounds like' (homophone) clue.
'infection' becomes 'sty' (sty is a kind of infection).
'sty' is a homophone of 'STYE'.
Can you help me to learn more?
(Other definitions for stye that I've seen before include "Red eye" , "irritation to the viewer" , "pain for the observer" , "Infection on the edge of the eye" , "Observer's problem" .)