• (a.) Having equal perimeters of circumferences; as, isoperimetrical figures or bodies.
I`so·per`i·met'ric·al adjective [ Greek ...; ... equal + ... circumference: confer French isopérimètre . See Perimeter .] (Geom.) Having equal perimeters of circumferences; as, isoperimetrical figures or bodies. 
In geometry, isoperimetrical is a term applied to figures which have equal circumferences or perimeters.