volumo

Take the gloss narrowly. In careful Esperanto a volumo is a physically bound book, one of the several that together make up a longer work: the third volumo of an encyclopaedia, the two volumoj of a collected edition. It is a thing on a shelf, not a quantity.

The two senses English piles onto the same word live elsewhere. The space a body occupies is volumeno - the geometrical volume, the one measured in cubic metres. Loudness is laŭteco, built from laŭta and the -ec- suffix, or sonforteco if you want to be technical about it. Asking someone to turn down the volumo will be understood, because everybody knows what you mean, but it is an English sentence wearing Esperanto endings.

Now the seam, which is a trap and a gift at once. The -um- in the middle looks exactly like the suffix that means "something to do with the root, and I decline to say what", the one covered in -um and word formation. It is not. Volum- is one borrowed root and the word is not vol- plus -um- plus -o. And yet the history behind it is real: Latin volumen was formed from volvere, to roll, which Esperanto also holds as volvi. So volumo and volvi are genuinely relatives - they simply became relatives in Latin, two thousand years before Esperanto existed, and the joint no longer opens.