biconvex

The other is Google Cardboard: a nifty kit that sells for $15 and that holds a smartphone in place in front of biconvex lenses.

Tube of corolla cylindrical, enlarging above; upper lip arched, compressed, straight in front; the lower erect-spreading, biconvex, 3-lobed at the apex.

Convex on both sides; as, a biconvex lens.

The lens is biconvex in diurnal mammals, but in nocturnal and aquatic it is spherical.

The red blood-corpuscles are invariably oval disks, with a central nucleus which causes a slight swelling; hence they are oval and biconvex.