praulo

A word with no root in it at all. Praulo is pra- plus -ul- plus the noun ending, and that is the entire word. Two affixes and a vowel. Esperanto lets you do this, English does not, and it is one of the moments where the machinery of the language is on open display: a prefix meaning further back and a suffix meaning person, glued together, give you the person further back. An ancestor.

Pra- is official, and here is the proof. It is one of the ten prefixes printed in the Fundamento of 1905, alongside bo-, dis-, ek-, eks-, fi-, ge-, mal-, mis- and re-. That means it belongs to the untouchable text and cannot be argued about, which the unofficial affixes article explains is a narrower guarantee than most learners assume but a real one.

It does two jobs. On kinship it adds a generation, and it stacks: avo gives praavo, a great-grandfather, and prapraavo is perfectly readable. On anything else it pushes the thing back to its earliest form: prahistorio, praarbaro for old-growth forest, pralingvo for a proto-language, pratempo. The pra- page has the full treatment.

And the matching pair. Posteulo at rank 2402 is built exactly the same way, out of post-, after, and the same -ul-: the person who comes after, a descendant or a successor. Praulo and posteulo are a matched set, one facing each direction, and neither needed a root to be invented for it. This is what people mean when they say Esperanto vocabulary compounds, and it is a better demonstration than malbona.