means To throttle is either to choke or strangle someone by the throat, or to control the flow of fuel and power to an engine — and by extension, the amount of anything allowed through.

from From Middle English 'throtelen,' to choke, built from 'throte' (throat) — the same word that names the passage you'd be squeezing. So strangling came first; the engine sense is a metaphor borrowed centuries later, when inventors needed a word for the valve that lets an engine breathe or chokes it down. To throttle a machine is, quite literally, to grab it by the throat.