As a adjective planar
is of or pertaining to a plane.
As a noun ring is
a circumscribing object, (roughly) circular and hollow, looking like an annual ring, earring, finger ring etc or
ring can be the resonant sound of a bell, or a sound resembling it or
ring can be (algebra) an algebraic structure which consists of a set with two binary operations, an additive operation and a multiplicative operation, such that the set is an abelian group under the additive operation, a monoid under the multiplicative operation, and such that the multiplicative operation is distributive with respect to the additive operation.
As a verb ring is
to surround or enclose or
ring can be of a bell, to produce sound;.