Suffixes -ar-, -er-.
The suffix "-ar-" signifies a collection of the persons or things named,
as "arbo", a tree, "arbaro", a wood; "homo", a human being, "homaro",
mankind; "militisto", a soldier (from "milito", war), "militistaro",
an army; "vorto", a word, "vortaro", a dictionary ("vortareto", a
vocabulary); "aro", a flock, "anaro", a company, troop.
"-er-" signifies a particle, or one of things of which the name denotes
a mass, as "greno", corn, "grenero", a grain of corn; "polvo", dust,
"polvero", a speck of dust; "pulvo", gunpowder, "pulvero", a grain
of gunpowder; "hajlo", hail, "hajlero", a hailstone; "negxo", snow,
"negxero", a snowflake; "koto", mud, "kotero", a speck of mud or dirt.