Sickly describes someone who gets sick often or seems weak and unhealthy. A sickly child might catch every cold that goes around school and take longer than others to recover. In older books, you might read about a sickly character who spends much of their time resting indoors, missing out on activities that healthier children enjoy.

The word can also describe something that looks or seems unhealthy. A plant with drooping, pale leaves looks sickly. A sickly smell might be unpleasantly sweet or suggest decay. When someone's face has a sickly pallor, their skin looks pale and grayish, as if they might be ill.

Sometimes people use sickly to describe colors or lights that seem wrong or unnatural, like a sickly green glow or sickly yellow lighting that makes everyone look unwell.

The word carries a sense of ongoing weakness rather than a temporary illness. Having the flu for a week doesn't make someone sickly, but missing school regularly because of one infection after another might. Modern medicine and better nutrition mean fewer children are sickly today than in the past, when diseases like tuberculosis and malnutrition were more common.