Mathematically, congruent means having the same size and shape, being identical in form. The antonyms are incongruent and incongruence. Congruous means to be in agreement or harmony usually in an aesthetic sense. It is rarely used, while its antonym, incongruous, is more common.

The distinction is slight, as the meanings are nearly identical. However, the former term is usually employed quantitatively, while the latter word is generally used qualitatively. The noun congruence and its adjectival form congruent refer to agreement or coincidence.

Congruity refers to the state of being in harmony or agreement, while congruence pertains to the quality of being identical in shape, size, and form, especially in geometry. Congruity focuses on harmony; congruence focuses on identical properties.