Not exactly perky, but rather sickly (5)
I believe the answer is:
peaky
'rather sickly' is the definition.
(I've seen this before)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for peaky that I've seen before include "Rather sickly" , "Slightly unwell" , "Seedy" .)