An Etymological Dictionary of Astronomy and Astrophysics

1. Agreeing; accordant.
   

2. Math.: → congruent number.
   

3. Geometry: → congruent angles, → congruent circles, → congruent line segments, → congruent polygons, → congruent triangles.

Etymology (EN): Congruent “suitable, proper,” from L. congruentem (nominative congruens) “agreeing, fit, suitable,” p.p. of congruere, literally “to come together, agree, correspond with,” from → com- “with” + a lost verb *gruere, *ruere “fall, rush.”

Etymology (PE): Damsâz “agreeing, consenting, harmonious,” maybe from hamsâz “unanimous,” → compatible.