Interloper

 WORD OF THE DAY

interloper / noun / in-ter-LOH-per

Definition
1a: one that interlopes
1b: one that intrudes in a place or sphere of activity
1c: an illegal or unlicensed trader

Examples
"For decades, physicists have suspected an interloper. A reclusive, hypothetical subatomic particle might be creeping into studies of neutrinos, nearly massless particles with no electric charge. A new study casts doubt on that idea…."
— Emily Conover, Science News, 27 Oct. 2021

The interloper has been vanquished, her family is safe, and her husband is in her arms again.
— Nylah Burton, refinery29.com, 11 Nov. 2021

Did You Know?
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.