Guard is the basis of a family of words pertaining to protection; these terms are listed and defined in the post below.
Guard, from the French verb garder (formerly also spelled guarder and warder), meaning “defend” and related to the Old High German term warten, meaning “take care,” has several senses: It refers to someone (or a group) assigned to protect someone or watch something or to the act of defending someone or keeping an eye on something, or the state of being protected.
It also pertains to a protective component or device, to an athlete who has a defensive or protective role in competition, or to a defensive attitude, position, or state. One can be said to be on guard, or in a state of readiness, or to be off guard; the latter phrase is generally seen in the phrase “catch (or “caught”) off guard.” It is also a verb, and the adjective is guarded, guardedly is the adverbial form, and guardedness describes the state of being alert.
Guard appears in the open compound “guard dog” and the closed compound guardrail. It is the root of guardian, a word describing a person in a protective role (such as an adult who serves as a surrogate parent for a minor); the state of being a guardian is guardianship. The phrase “guardian angel,” based on the notion of a protective supernatural being, now often refers to a flesh-and-blood person in such a role.
“En garde,” taken directly from French, means “on (your) guard” and serves in fencing as a spoken warning for competitors to be prepared to defend themselves.
Regard, as a noun meaning “consideration” or “judgment” (with the antonym disregard) or, as a verb, “consider” or “judge,” is from the French verb regarder, meaning “look at.” As a noun, it also has the sense of “respect,” and as such is used in correspondence in plural form as a sign-off. Self-regard refers to consideration of oneself or one’s interests. Regardless is an adjective with the sense of “in spite of” or “without consideration”; irregardless is an unfortunate and unnecessary variant careful writers will assiduously be on their guard to avoid.
An advance guard or vanguard was originally a military unit that preceded the main body of troops into battle; the latter term now usually refers to a person or group at the forefront of a movement. Avant-garde is the French equivalent, borrowed into English with that sense but now figuratively describing an innovative artist, musician, or writer, or a work of art or literary or musical composition that is ground-breaking, or an entire creative movement considered as such. A rearguard, by contrast with a vanguard, protects a retreating force, and by analogy the word also pertains to resistance to an overwhelming phenomenon. “Honor guard” refers to a member of the military who has a ceremonial function or to a small unit of military personnel with such a role.
Closed compounds with guard as the second element include bodyguard, referring to an individual assigned or hired to protect someone or to a group or unit in that role; lifeguard, originally a synonym for bodyguard but now the designation for a person trained to rescue people from a body of water when they are at risk of drowning; and safeguard, which means “something that provides protection.”