A vocal performance with no instrumental accompaniment.
Singing solely or mainly without instrumental accompaniment.
Related to a form of purely vocal music mostly associated with American college performance groups.
In a manner of a choir with no instrumental accompaniment; literally, "in the style of the (Sistine) Chapel (in Rome)", such as a musical Mass done a cappella.
A shrill noise, especially made by a voice or bird; a yell, scream, or call.
A complaint or objection.
A four-digit transponder code used by aircraft for identification or transmission of emergency signals.
A warning message indicating a possible error.
An issue or complaint related to aircraft maintenance.
The American night heron.
To make a squawking noise; to yell, scream, or call out shrilly.
To produce a warning message, indicating a possible error.
To set or transmit a four-digit transponder code. (Normally followed by the specific code in question.)
To report an infraction; to rat on or tattle; to disclose a secret.
To speak out; to protest.