An enforcer of maritime law, in charge of policing the seas within territorial waters(noun)
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Use "coastguard" in a sentence
"We don't really have a problem with maritime smuggling in the UK, the USA does, hence why their Coast Guard, which is really more of a "guard of the coast" than what we associate with the term coastguard here, is a small navy and ours is a small government agency that supplements RNLI and RAF rescue efforts."
"Dennis went on what he called coastguard duty, and watched the sea and shores with the untiring loyalty of a faithful dog."
"It is ... a matter of some family pride that my father was for many years a member of the auxiliary coastguard, which is now a volunteer coastguard, on Islay."