Indistinct sign of illness (5)
I believe the answer is:
faint
'indistinct' is the definition.
(similar in meaning)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for faint that I've seen before include "Swoon - pale" , "(Of a chance) slight" , "dull" , "woozy" , "Dim -- swoon" .)