A concave surface or curve. / The vault of the sky. / One of the celestial spheres of the Ptolemaic or geocentric model of the world.

To render concave, or increase the degree of concavity.

(music) A piece of music for one or more solo instruments and orchestra.

The end, finish, close or last part of something. / The outcome or result of a process or act. / A decision reached after careful thought.

The practice of keeping secrets. / The condition of being hidden or concealed. / (military) protection from observation or surveillance.

A genre of art in which the transmission of ideas is more important than the creation of an art object

Of, or relating to concepts or mental conception. / Existing only in the imagination. / Of or relating to conceptualism.

A short and/or incomplete realization of a certain method or idea to demonstrate its feasibility. / (software engineering, perhaps nonstandard) A proof of technology or pilot project.

(music) A musical instrument, like the various accordions, that is a member of the free-reed family of musical instruments, typically having buttons on both ends.

to become compressed into a shape reminiscent of a concertina / to be drawn closer and farther apart repeatedly, or up and down, as if situated on a working concertina's folds