hiss

Hiss is a sound that resembles a sharp, elongated “s” and is produced by air flowing through a narrow constriction, creating turbulence. In English, the term is used both for a literal sound and for any noise that has a similar sibilant quality. The hiss is typically a voiceless sound, dominated by a high-frequency fricative component, and can vary in pitch and duration.

The most familiar natural hiss comes from snakes. When alarmed or threatened, many snakes force a rapid, directed stream of air through a partly open mouth, producing a sustained, hiss-like noise. In snakes the sound is largely air-driven and may be augmented by soft tissue vibrations, but it does not require vocal cords in the same way as many other animal sounds. Other animals, such as some cats, can produce hiss-like warnings by expelling air through an open mouth and glottis, sometimes with limited vocalization.

Non-biological hissing occurs when pressurized gas or steam escapes through a small opening, or when fluids flow past obstructions. Mechanical systems—brakes, tires, radiators, pipes, and valves—often emit a hiss due to turbulence. In audio and electronics, “hiss” describes a background noise component, such as tape hiss or receiver hiss, caused by random electrical or thermal noise.

Etymology-wise, hiss is an onomatopoeic word designed to imitate the sound. It is commonly used in literature and media to convey the presence of something sharp, dangerous, or persistent, and can be employed as a symbol of disapproval when crowds hiss.