Plural of Arms
For the countable body-part and related ordinary senses, “arm” forms the regular plural “arms.” The same spelling “arms” also has a lexical plural meaning weapons and military equipment, as in “small arms” or “lay down arms.” Identify the sense before treating an occurrence as a simple body-part plural.
The ordinary plural of body-part “arm” is “arms.” Separately, “arms” is a lexical plural noun meaning weapons or military equipment.
Key details
Choose the right form
| Meaning / situation | Form / construction | Decision |
|---|---|---|
| one body part / component | arm | Singular countable noun. |
| several body parts / components | arms | Regular plural. |
| weapons / military equipment | arms | Lexical plural noun. |
Quick tests
Plural-choice test
Are you counting more than one ordinary arm?
If yes: Use regular plural “arms.”
If no: If it means weapons/equipment, treat “arms” as that lexical plural sense.
Caveat: Fixed expressions can have their own meanings and should not be edited from morphology alone.
Examples
She raised both arms.
Two body parts take the regular plural.
The treaty limits the transfer of arms.
Weapons use the lexical plural sense.
He injured one arm.
One body part takes singular “arm.”
Further guidance
Core difference
Use “arms” as the regular plural of body-part “arm”; also recognize lexical weapons “arms” as a separate plural sense.
Fast Test
Ask whether the noun counts body parts/branches/components or means weapons/equipment.
Usage Boundary
Do not force the weapons sense into a singular “an arm” unless that specific separate noun sense is actually intended.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- ARMS | English meaning - Cambridge Dictionary (opens in a new tab)Cambridge University Press · Cambridge labels arms a plural noun for weapons and military equipment.
- ARM | English meaning - Cambridge Dictionary (opens in a new tab)Cambridge University Press · Cambridge separately treats ordinary body-part arm as countable with regular plural arms, supporting the distinction from lexical weapons arms.