Calyx and Cavity

Calyx noun - (botany) the whorl of sepals of a flower collectively forming the outer floral envelope or layer of the perianth enclosing and supporting the developing bud; usually green.

Cavity and calyx are semantically related. In some cases you can replace term "Cavity" with "Calyx", this nouns are similar.

Cavity noun - A sunken area forming a separate space.

Calyx and cavity are semantically related. Sometimes you can use "Calyx" instead a noun "Cavity".