When an individual or an organization (such as a business or a local or state government) thinks that a governmental action is in violation of a constitutional limitation, s/he/it may file suit against the government (Federal, state, or local as the case may be). Such suits most often seek injunctions against continuation of the action, but sometimes damages, particularly under 42 U.S.C. § 1983. Also, persons accused of crime may argue that the law violates their Constitutional rights, or that some part of the enforcement procedure violated those rights. Such suits and court actions are the main way in which US Constitutional rights, including those in the Bill of Rights, are enforced.
Constitutional rights are almost never absolute. For example the rights of free speech and a free press in the First Amendment are stated in rather absolute terms, but libel and defamation laws are constitutionally permitted, although they were somewhat limited by the decision in NY Times vs Sullivan, 376 U.S. 254 (1964). Regulation of the "time, place, and manner" of speech is also permitted. Although the same amendment guarantees Free Exercise of religion, laws prohibiting human sacrifice and polygamy are constitutional. the Fourth Amendment limits search and seizure, but search warrants are still issued every day. The Second Amendment does not mean that no regulation of guns can ever be constitutional.
For much of our history, the clause
A well regulated Militia, being necessary to the security of a free State
was considered to be a condition of the right, and no individual right to own firearms was guaranteed to those in no way connected with a governmentally authorized militia (private militias were not considered "well regulated"). Since DC. v. Heller that view has changed, but that does not make all regulation of guns impossible under the Constitution. Moreover, a number of legal scholars think that Heller was wrongly decided, and should be reversed. The Supreme Court could decide to do that, although the current Justices have not indicated any such intention.
The U.S. Supreme Court in McDonald v. Chicago, 561 U.S. 742 (2010) said, quoting DC vs Heller:
It is important to keep in mind that Heller, while striking down a law that prohibited the possession of handguns in the home, recognized that the right to keep and bear arms is not “a right to keep and carry any weapon whatsoever in any manner whatsoever and for whatever purpose.”
We made it clear in Heller that our holding did not cast doubt on such longstanding regulatory measures as “prohibitions on the possession of firearms by felons and the mentally ill,” “laws forbidding the carrying of firearms in sensitive places such as schools and government buildings, or laws imposing conditions and qualifications on the commercial sale of arms.”
The question suggests that a dictionary definition of "infringe" implies that the right is utterly absolute. This contradicts the Supreme Court statement holding above, and all of our history of constitutional law. To the best of my knowledge there is no provision or right that does not have limited exceptions or room for interpretation. Justice Black's absolutist view of the Bill of Rights, and particularly of the rights of Freedom of Speech and of the Press, never carried a majority of the Court nor of the country.
To "infringe" a right is to violate it, to fail to respect the right. But that leaves the question of just what the right guarantees. Suppose a law requires a permit to own a gun, but that permit is granted to anyone on filing an application and payment of a small fee. Would that infringe the right? Suppose a similar permit requirement, but one excluding felons, persons on parole, and persons under a domestic violence restraining order. Would that infringe? Suppose a requirement that a would-be owner first pass a firearms safety class, which most people pass easily. Would that infringe? There are many such questions, and current case law has not settled all of them. The first two above seem to be answered "No" by the US Supreme Court.
By the way, the history of the debates does not suggest that the ability of individuals to defend themselves, particularly against the government, was a significant concern in drawing up the Second Amendment. The focus was largely on Federal funding of state militias (later the National Guard). Other data shows that gun ownership was comparatively rare at the time of the adoption of the Bill of Rights.