A unit of matter; an atom; also, an individual.

【哲】物质单元；原子；个体。

One of the smallest and simplest of living creatures, supporting life in water.

单细胞生物(常存于水中，如鞭毛虫类之原生动物)。

Formerly, a simple organism or cell.

【生物】单机体；细胞。