Dihedral
/daɪˈhiːdrəl/noun
Relating to two intersecting plane surfaces or to a plane angle formed by two lines or planes.
Did you know?In classical Greek, the *hedra* root behind *dihedral* also appears in words tied to sitting and seating, so this “math word” carries the ghost of a body at rest.
Etymological Timeline
Proto-Indo-European
PIE
*sed-
“to sit, settle”
Ancient Greek
Greek
hedra
“seat, base, sitting place”
Ancient Greek
Greek
di- + hedra
“two seats; two faces / two planes”
Late Latin / Medieval Latin
Latin
dihedrus
“having two faces or two planes”
17th Century
English
dihedral
“having two sides or two plane faces”
Explore more surprising origins