estraro

Read it from the right, one piece at a time: estr + ar + o. The -o makes it a noun, -ar- makes a collection, and -estr- is the head or chief of whatever stands in front of it. A collection of heads: a governing board.

This is the example the apposition article uses to make its point, and the point is a strange one. Estraro is built out of two suffixes and an ending, with no root of its own. That is legal because in Esperanto every official affix is also a full word: -estr- stands alone as estro, a boss, exactly as -ar- stands alone as aro, a set. So you can call it a stack of two suffixes, or you can call it estro plus -ar-, and both readings land on the same meaning. Nothing hangs on which you prefer - what matters is that neither reading needs a dictionary.

In practice it is the club word. Esperanto associations, and the movement generally, are run by an estraro; the members are estraranoj, and the person in the chair is the prezidanto. Compare komitato, which is a borrowed root and means a committee in the wider sense - a body appointed to do one job. An estraro is the standing leadership of an organisation; a komitato may be assembled for an afternoon.

The pattern generalises immediately. Lernejestro is a headteacher, ŝipestro a captain, urbestro a mayor, and each of those can take -ar- in turn if you need the plural body rather than the person.