One who or that which darkens.

plural of darkener

(transitive) To make dark or darker by reducing light. / (intransitive) To become dark or darker (having less light).

simple past tense and past participle of darken

Made dark or lightproof by the exclusion of light. / Having an absence of light, such as at night-time.

present participle of darken

The act of something becoming darker.

Third-person singular simple present indicative form of darken

plural of darkening

(physics, astronomy) Of a star, specifically its equator: darker due to gravity darkening.