centimetro

Here the seam is genuine, and it is worth taking the moment. This chapter is full of long borrowed words that look decomposable and are not - instituto, majesta, konferenco, rigida. Centimetro is the opposite case. It is centi- plus metro, and both halves are live.

Centi- is not an Esperanto affix in the Zamenhofian sense; it is the international SI prefix for a hundredth, and Esperanto takes the whole metric prefix set as given: mili-, centi-, deci-, deka-, hekto-, kilo-. That is why kilogramo parses the same way - kilo- on gramo - and why, once you have both words, you can read kilometro, milimetro and centigramo without being taught any of them. Six prefixes and two roots cover most of the measuring you will ever do.

The number under it. Cent is the Esperanto numeral cent, a hundred, and centi- is transparently from the same Latin centum. The relationship is a happy accident of borrowing rather than a designed feature, but it makes the prefix easy to hold: centimetro is the hundredth-metre.

Using it. Measurements take the accusative when they answer "how much": kreski kvin centimetrojn, esti dudek centimetrojn longa. Abbreviated, it is cm, read aloud as centimetro. And note that Esperanto puts the unit after the number with no preposition - tri centimetroj, never tri de centimetroj.