evolvent 切展线
渐开线
渐屈线
渐伸线
Evolvent \E*volv"ent\, n. [L. evolvens, -entis, unrolling, p.
pr. of evolvere.] (Geom.)
The involute of a curve. See {Involute}, and {Evolute}.
Involute \In"vo*lute\, n. (Geom.)
A curve traced by the end of a string wound upon another
curve, or unwound from it; -- called also {evolvent}. See
{Evolute}.