Definition of biplanes:
(n) :
(aviation) An airplane that has two main wings, one above the other and supported by struts.
(adj) :
(aviation) Having, or consisting of, two superposed planes, aerocurves, etc.
(adj) :
Composed of, or relating to, two planes (flat surfaces extending infinitely in all directions).
(v) :
(intransitive, rare) To fly in a biplane.