hexagon (n.)

before vowels and in certain chemical compound words hex-, word-forming element meaning "six," from Greek hexa-, combining form of hex "six," from PIE root *sweks- (see six).

Proto-Indo-European root meaning "knee; angle."

It forms all or part of: agonic; decagon; diagonal; geniculate; genuflect; genuflection; -gon; goniometer; heptagon; hexagon; knee; kneel; octagon; orthogonal; pentagon; polygon; trigonometry.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit janu, Avestan znum, Hittite genu "knee;" Greek gony "knee," gōnia "corner, angle;" Latin genu "knee;" Old English cneo, cneow "knee."

1570s, from hexagon + -al (1). Related: Hexagonally.