interloper

When English speakers combined "inter-" with "-loper" in the late 1500s, they already had a word landloper (now archaic) for "a person who runs about the land" (in other words, a vagrant). The "-loper" part of "interloper" is related to Middle Dutch and Old English words meaning "to run" and "to leap." An "interloper" is essentially one who jumps into the midst of things without an invitation to do so. In its earliest uses, "interloper" referred specifically to one who interfered in trade illegally - that is, a trader who trespassed on the rights or charters of others. Sometimes "interloper" even referred to a ship employed in illegal trading. But the word quickly took on extended use, coming to refer not just to intrusion in trade but also in personal affairs or other matters.