Chambers 20th Century Dictionary(0.00 / 0 votes)Rate this definition: Sibilance. sibâ²i-lans, n. a hissing soundâalso Sibâ²ilancy.âadj. Sibâ²ilant, making a hissing sound.ân. a sibilant letter, as s and z.âv.t. Sibâ²ilÄte, to pronounce with a hissing sound.ân. SibilÄâ²tion, a hissing sound.âadjs.
Definition: A delta wave is a type of high amplitude brain wave found in humans. Delta waves have a frequency from one to four hertz and are measured using an electroencephalogram (EEG). These brain waves are thought to emerge from the thalamus and are generally associated with slow-wave sleep (during stages three and four of the stages of sleep.
beta waves in Medicine Expand. beta rhythm n. The second most common waveform occurring in electroencephalograms of the adult brain, characteristically having a frequency from 13 to 30 hertz. It is associated with an alert waking state but can also occur as a sign of anxiety or apprehension. Also called beta wave.