meter

Meter comes from Greek metron, "measure." That noun is old and basic, used for a standard, a limit, and a measured quantity in texts from the classical period. Greek poetry then used the same idea for measured arrangement in verse. Rhythm was understood as counting and proportion before it became a schoolroom term.

Latin borrowed the word as metrum, especially for poetic measure. Roman grammarians and poets used it for patterns such as hexameter and pentameter. In that setting, meter named not an instrument but the structure of syllables and beats. The word was technical, compact, and durable.

French passed on metre, and English adopted meter in the later Middle Ages and early modern period. English spelling eventually split: meter became usual in American English for both poetic measure and many measuring devices, while metre remained common in British usage for verse and length. That later split is modern. The older inheritance is the same Greek noun.

Because metron meant measure in the widest sense, English built new uses with ease. A gas meter and poetic meter look unrelated, but both descend from the idea of counted order. One measures usage; the other measures sound. The old Greek sense still holds them together.