evolute
Concise Oxford English Dictionary © 2008 Oxford University Press:
evolute /ˈiːvəl(j)uːt, ˈɛv-/
▶noun Mathematics a curve which is the locus of the centres of curvature of another curve (its involute). ▶adjective Zoology & Botany rolled outwards at the edges.
'evolute' also found in these Oxford entries:

