(intransitive) To fail after a promising beginning; to disappoint expectations.

(optics) A disk of high-quality quartz glass having at least one side ground and polished with a deviation in flatness less than 50 nanometers all over, and a surface quality of 5 microfinish or less; used, in an interferometer, to measure the flatness of other surfaces.

(simile) Particularly or extremely flat.

Alternative spelling of mudflat.

(mathematics) Any Riemann space in which the metric tensors are constants throughout

(rail transport) An at-grade junction between two crossing railroad tracks.

(UK) a rate (typically of money) that does not vary over time

(UK) Being or relating to a flat rate.

(chiefly American spelling) Alternative spelling of flat tyre

A tyre of a motor vehicle that is deflated, especially one deflated because of a puncture when in use.