skleros

Skleros is a Greek root meaning "hard" or "firm." In scientific and medical language it is primarily encountered as the combining form sclero- or scler-, rather than as a stand-alone word. The root derives from the Greek noun skleros (σκληρός).

In biology and medicine, skleros forms terms that describe hardened tissues, structures, or processes. Examples include:

- sclera, the tough, white outer coat of the eye, whose name reflects its hardness; the term ultimately derives from Greek sklera and Latin sclera.

- sclerenchyma, a plant tissue providing mechanical support, formed from sclero- + enchyma.

- scleroderma, a connective tissue disease characterized by thickening and hardening of the skin, from skleros + derma.

- sclerosis, the abnormal hardening of tissue or an organ, as in atherosclerosis or multiple sclerosis.

- sclerite, a hardened plate in the exoskeleton of arthropods.

- sclerotium, a compact hardened mass of fungal mycelium capable of giving rise to growth under favorable conditions.

- sclerotization, the chemical hardening of insect cuticle through cross-linking of proteins.

Notes on usage: sclero- is the common Latinized form used in nomenclature and textbooks, while skleros appears mainly in linguistic or historical discussions about Greek-derived vocabulary. The term is a productive root across disciplines, illustrating how a single ancient meaning—hardness—shaped many modern scientific words.