Taken on its own, the word “estro” means a leader (or, more colloquially, a boss or a chief). You can put -estr- into a word to create specific types of leaders.

Sxipestro (sxip- + -estr- + -o) = Ship’s captain
Lernestro (lern- + -estr- + -o) = Principal, professor, etc.
Urbestro (urb- + -estr- + -o) = Mayor

Perhaps your previous Esperanto studies bring to mind the word “fenestro.” We can break it apart to show fen-, -estr-, and the -o suffix. We know that “fenestro” actually means “window” (which Zamenhof probably adapted from the Latin word “fenestra,” from which English derives its oddly specific verb “defenestration” – to eject from a window!). Given what -estr- means, the word “fenestro” doesn’t seem to make much sense. A master of “fenoj?”

It’s likely unintentional, but the etymology of “fenestro” ends up working out quite nicely. The word “feno” in Esperanto means “a chinook,” which is a type of wind. A window controls whether or not one’s room experiences the wind or not – which may well be why “wind” fits into the word in English. With this in mind, perhaps the “fenestro” is meant to be the master of the winds – something that controls them to keep your papers from blowing off of your desk, or to keep insects from flying in your window as you drive to work.