-on-

-on- cuts a numeral into a fraction. Du gives duono, tri gives triono, kvar gives kvarono, dek gives dekono, cent gives centono. The noun form in -o names the part, duona describes it and duone says how something was done. Whatever the fraction is a fraction of arrives with de, as in duono de la pano.

You already own duono from the core word list, so you have been using the machinery for a while without meeting the suffix.

Its mirror is -obl-, and they differ by three letters in the middle of a word, which is where errors live. Duona is half as much. Duobla is twice as much. Read the whole suffix before you commit to a number.