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What does the suffix “-isto” mean in Esperanto?

Add -isto to a root and you get the person whose job or habit it is: this clip alone gives kantisto (singer, from kanti, “to sing”), instruisto (teacher, from instrui, “to teach”), and kuracisto (doctor, from kuraci, “to heal”). It is one of Esperanto’s most productive suffixes — learn the root verb and the profession word comes for free, no separate vocabulary to memorize.

The same clip adds -in- for the female form before the final -o: instruisto → female instruistino, kuracisto → kuracistino. In practice, many Esperanto speakers now treat the plain -isto form as gender-neutral by default (the way “actor” has drifted in English), so the -in- form is used when the distinction actually matters, not automatically. The suffix isn’t limited to jobs, either — Esperantisto itself is built the same way: a person who does/uses Esperanto.