tachy

Tachy is a combining form derived from the Greek tachys meaning swift or rapid. It is used as a prefix in various scientific and medical terms to indicate an increased rate of something.

In medicine, tachy- terms describe rapid physiological processes: tachycardia refers to an abnormally fast heart rate; tachypnea to rapid breathing; tachyarrhythmia to irregular or rapid heart rhythms; tachyphylaxis to a rapid diminution in response to a drug after initial exposure.

In other fields, the prefix appears in concepts invoking speed: tachyon is a hypothetical particle that travels faster than light; a tachometer is an instrument that measures rotational speed, commonly found in vehicles; a tachymeter is a scale on some watches and instruments for calculating speed based on elapsed distance.

The prefix emphasizes speed rather than a qualitative state. It contrasts with brady- meaning slow. In clinical contexts, thresholds vary by condition; for example, a resting heart rate above 100 beats per minute is commonly used as a rough criterion for tachycardia in adults.

See also: tachy- combining form; tachycardia; tachypnea; tachyon; tachometer; tachymeter; tachyphylaxis.