Body part is viewed under infrared (4)
I believe the answer is:
iris
'body part' is the definition.
(iris is a kind of body part)
'is viewed under infrared' is the wordplay.
I cannot quite see how this works, but
'is' is within the answer.
'infrared' could be 'ir' (I've seen this in other clues) and 'ir' is present in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for iris that I've seen before include "Flowers in the eye?" , "is 21[WOMAN], perhaps" , "bit of a looker" , "Lily" , "Woman" .)