Binnick's Languages and Linguistics Blog

This is a quote from Word Formation in Esperanto by Ed Robertson.

Compounding is the joining together of words or stems to form longer words, for example doorknob and biology. There are some technical differences between the two types of compound exemplified by these words, but let’s not bother with that here.

Derivation is the forming of a new word by adding an affix to a base or stem, which can be a root or a longer form, either a compound or a derived form. Examples include away, baker, unusual, and reintroduction.

The reason there is no such dividing line in Esperanto is that with only a small number of exceptions, Esperanto affixes can be used as roots. For example, nouns are formed by adding –o to a stem. Domo means ‘house, home’. Adjectives are formed by adding –a, so doma means ‘domestic’. But o can itself be a root: oo means ‘thing’. Affixes like –ec and –ul can also be roots. Regxo is ‘king’, regxeco ‘royalty’; bona means ‘good’, bonulo ‘a good person’. Eco means ‘quality’ and ulo ‘person’.

Thus although Esperanto is usually described as an agglutinative language, it is possible to describe it as an unusual kind of synthetic language. In any case, this is one respect in which Esperanto is quite unlike natural languages, at least the ones I’m familiar with.