unexplained
UK: ˌʌnɪkˈspleɪnd | US: ˌʌnɪkˈspleɪnd
adj. not made clear or accounted for; lacking an explanation
The word "unexplained" combines the negative prefix "un-" (Old English "un-," meaning "not") with the verb "explain" (from Latin "explanare," meaning "to make plain or flat," via Old French "explainier"). The suffix "-ed" marks the past participle form, turning it into an adjective. The logical progression reflects a state where something has not been made clear or resolved.
The sudden disappearance of the artifact remains unexplained.
Scientists are puzzled by the unexplained phenomenon in the experiment.
Her unexplained absence worried her colleagues.
The report left many questions unexplained.
Unexplained noises in the old house frightened the children.