evolute

[ev-uh-loot or, esp. British, ee-vuh-] /ˈɛv əˌlut or, esp. British, ˈi və-/
noun, Geometry
1.
the locus of the centers of curvature of, or the envelope of the normals to, another curve.
Compare involute (def 5).
Origin
1720-30; < Latin ēvolūtus (past participle of ēvolvere to roll out, unfold, evolve)
British Dictionary definitions for evolute

evolute

/ˈɛvəˌluːt/
noun
1.
a geometric curve that describes the locus of the centres of curvature of another curve (the involute). The tangents to the evolute are at right angles to the involute
adjective
2.
(biology) having the margins rolled outwards
Word Origin
C19: from Latin ēvolūtus unrolled, from ēvolvere to roll out, evolve