Sickliest

adjective

1. Frequently ill or in poor health.

   "a sickly child"

2. Not in good health; (somewhat) sick.
3. (of a plant) Characterized by poor or unhealthy growth.
4. Appearing ill, infirm or unhealthy; giving the appearance of illness.

   "a sickly pallor"

5. Shedding a relatively small amount of light; (of light) not very bright.