Interloper
Interloper (?; 277) , noun
[Prefix inter- + Dutch looper a runner, from loopen to run; akin to English leap. See Leap, and compare Elope.]
One who interlopes; one who unlawfully intrudes upon a property, a station, or an office; one who interferes wrongfully or officiously.
The untrained man,... the interloper as to the professions.