n. 1
The part of a sword that protects the wielder's hand.
n. 2
A person who, or thing that, protects or watches over something.
border guard, prison guard, security guard
v. 1
To protect from danger; to secure against surprise, attack, or injury; to keep in safety; to defend.
All of the mountain passes are guarded by troops.
v. 2
To keep watch over, in order to prevent escape or restrain from acts of violence, or the like.

Related words

Phrases: prison guard on guard stand guard crossing guard chain guard advance guard axle guard security guard

Forms

Plural: guards → crossguards, quillons, safe-guards, precautions…
Past participle: guarded
e.g. guarded → defended, protected, secured, checked…

Guard, Keep or Defend?

Keep in the sense of guard or defend implies that the defense is effectual.

J. C. Fernald, English Synonyms and Antonyms (1914)

Use in printed books, per decade from 1850 to 2019.

3 letters: arm¹
4 letters: keep¹, hold¹, wing¹, tend¹, ward¹, curb¹
5 letters: watch¹, check¹, cover², fence¹, armor²
6 letters: safety², screen¹, secure², defend², attend², shield¹, patrol², escort², refuge², armour², convoy², fender², picket², sentry²
7 letters: defense², protect², defence², conduct², shelter², bulwark², rampart², quillon²
8 letters: security⁴, guardian³, preserve², sentinel³, watchman²
9 letters: conductor³, protector³, palladium⁴, guardsman²
10 letters: protection³, precaution³, crossguard, watchwoman
11 letters: guardswoman
12 letters: watchfulness

The small number after each word is its number of syllables (cover² = 2 syllables).