Grammar : Plural Nouns

• Always with -s ending but before of singular meanings, example : series, news, means, economics, physics, mathematics
• Always with -s plural in singular form, example : towers, pyjamas, pliers.
• Never with -s but plural in meaning, example : cattle, police, gently, folk, traffic, machinery, equipment, crockery, people, luggage
• Double plural ; 1. plural in meaning : army, band, class, team, tribe, troop. 2. being more than group : armien, bands, classes, teams, tribes, troops.
• Singular in form : the moon can be either singular or plural in meaning. : army, staff, herd, and, tribe, crew, crowd, audience, team, litter, class, torup.
• Singular and plural forms are the same 

singular : dear of spring, sheep,  swine, datum, memorandum, radius, curriculum, genius, alumnus, thesis
Plural : dear of spring, sheep, swine, data, curricula, radi, geni, alumni, theses