h₂enk-ulo-
“bent, hooked, angled”angle, ankle, anchor, angular
Diminutive of *h₂enk- giving Latin angulus, English angle, ankle, anchor, angular.
Discussion
The PIE form *h₂enk-ulo- (bent, hooked, curved at an angle) derives from the root *h₂enk- (to bend), with the suffix *-ulo- forming a diminutive or adjectival derivative. The meaning is "the bent thing" or "having a bend" — a concept that produced vocabulary for hooks, corners, and the body parts where limbs bend.
Latin angulus (corner, angle — a point where two lines bend to meet) continues the root and gave English the geometric vocabulary: angle (the space between two meeting lines), angular (having sharp angles), rectangle (a right-angled figure), triangle (a three-angled figure), and quadrangle (a four-angled enclosure). The word England (from Latin Anglia, "the angled land" — named for the Angles, a Germanic tribe whose name may derive from Angul, the "hook" or "angle" of the Jutland peninsula from which they came) may be the most geographically consequential descendant.
Latin ancora/anchora (anchor — the hooked device that grips the seabed) enters through Greek ánkyra (ἄγκυρα, "anchor, hook"), giving English anchor. The related Greek ankýlos (ἀγκύλος, "crooked, curved") gave the medical term ankylosis (stiffening of a joint — the joint becoming permanently "bent").
English ankle (OE ancleow, from PGmc *ankulaz — the body's natural angle, the joint where the foot bends) continues the root natively. German Enkel (ankle) preserves the cognate.
The root's semantic coherence is impressive: every descendant refers to bending or the result of bending — whether geometric (angle), nautical (anchor), anatomical (ankle), or medical (ankylosis). The PIE speakers who named the act of bending generated a root that their descendants would apply to mathematics, navigation, anatomy, and national identity.