gremlin
UK[ˈɡrem.lɪn]US[ˈɡrem.lɪn]
n
An imaginary mischievous creature, especially one blamed for unexplained mechanical or electronic faults.
n
A person or thing that causes problems or mischief.
Etymology
The word 'gremlin' is a modern invention, first recorded in Royal Air Force slang around the 1920s. Aviators humorously blamed these imaginary, impish creatures for inexplicable engine troubles and mechanical gremlins during flights. While its exact linguistic birth is murky, it is widely believed to be a playful blend, perhaps drawing from the Irish 'gruaimín' (a gloomy little person) and echoing the mischievous sound of words like 'goblin'. From its specific aeronautical origins, the term expanded into general use to describe any unseen source of vexation, particularly in complex machinery, and later to any mischievous person or persistent problem.
Analysis
The word 'gremlin' is a simplex word. It is a 20th-century coinage with no clear, separable morphemes in its modern English form. Its origin is likely a blend or fanciful invention, possibly influenced by the Irish word 'gruaimín' (meaning 'ill-humored little fellow') or the obsolete English word 'grem' (to vex).
Examples
The pilot joked that a gremlin must have gotten into the navigation system.
I think there's a gremlin in my computer; it keeps crashing for no reason.
He's a little gremlin, always hiding his sister's things.