a sickly person or animal is weak, unhealthy, and often ill:
She looked pale and sickly.
2 especially British English
a sickly smell, taste etc is unpleasant and makes you feel sick:
A sickly smell clung to his clothes and hair.
a sickly colour or light is unpleasantly pale or weak:
The walls were painted a sickly green.
a pale, sickly moon
a sickly sweet perfume