The building blocks of English

Affixes

tachy-

Rapid.

Greek takhus, swift.

In medicine, tachycardia (Greek kardia, heart) is an abnormally rapid heart rate; tachyphylaxis (Greek phulaxis, act of guarding) occurs when repeated doses of a drug cause responses that are progressively and rapidly less effective; tachypnoea (US tachypnea) (Greek pnoē, breathing) is abnormally rapid breathing. A tachyon is a hypothetical particle that travels faster than light.