Plural of “army”

The plural of army is armies.

Why

"Army" comes from Old French "armee," from Latin "armata," meaning "armed," the feminine past participle of "armare," to arm — the word originally described an armed force in the broadest sense, whether on land or at sea, before narrowing specifically to land forces once "navy" split off as a separate term for naval forces. Since a consonant, m, immediately precedes that final y, the standard swap applies: y becomes i, and -es is tacked on, producing "armies."

That early overlap with naval forces is easy to forget, since "army" and "navy" now feel like completely distinct, unrelated categories, but both ultimately share the same underlying Latin sense of an organized armed force, only later dividing by domain, land versus sea, rather than by root meaning. The word entered English through Anglo-Norman military and administrative vocabulary following the Norman Conquest, part of the same broad wave of French governmental and military terms, including "soldier" and "battle," that reshaped English fighting vocabulary during the medieval period.

Usage note

"Armies" is standard in every context, from military history to the common figurative use describing any large, organized group ("an army of volunteers," "armies of ants"). Corporate and marketing writing has also picked up the figurative sense heavily ("an army of sales reps"), a usage some style guides now consider overused business jargon.

Military historians often distinguish "standing armies," permanent professional forces maintained even during peacetime, from temporary levies or militias raised only for a specific conflict, a distinction that became increasingly important in European history from the 17th century onward as nations shifted toward permanent professional militaries. The figurative use of "army" for any large, purposeful group has been productive in English for centuries, appearing in phrases as varied as "an army of lawyers," "an army of ants," and "an army of supporters," each treating the noun's core sense of an organized, numerous force metaphorically rather than literally. Chess terminology sometimes borrows "army" informally to describe one player's full set of pieces, a casual metaphorical extension of the word's core sense of an organized force arrayed for battle.

Common real mistakes

The usual consonant-plus-y misspelling, "armys," is the error to avoid; the figurative plural use (armies of something) sometimes strikes careful editors as clichéd if overused, though that's a style concern rather than a grammar one. Writers should also distinguish "army" from the broader "armed forces," since "army" technically refers to land forces specifically, while "armed forces" covers land, sea, and air branches together.

The wider pattern

"Army" shares its plural pattern with "country" and "city," and its shared Latin root with "navy" (both ultimately about being "armed" in a general sense) is a reminder that even words that now describe completely separate military branches can share a common ancestor once their meanings are traced back far enough.

Examples

• Two rival armies met on the battlefield at dawn.
• Historians compared the size of ancient armies across empires.
• Volunteer armies were quickly assembled at the war's outset.
• The documentary followed the movements of both armies in detail.
• An army of workers rebuilt the bridge within weeks.
• Several armies retreated as winter approached.
• The museum displayed uniforms from armies of different eras.
• Ant colonies function almost like miniature armies.
• Standing armies became more common in early modern Europe.
• The two armies negotiated a temporary ceasefire.
• Historians debated how supply lines shaped the fate of both armies.
• Reinforcements joined the army just before the final battle.
• Historians still debate why the armies clashed at that location.
• The two armies clashed again the following spring.
• Recruiters visited towns to build up the army.
• Supply shortages weakened both armies by winter.
• The general reorganized the army before the campaign.