The word "weasely" is a straightforward English derivation from the noun "weasel." The animal, the weasel, has long been culturally associated with traits of cunning, stealth, and elusive behavior due to its hunting habits and slender physique. By adding the adjectival suffix "-y," meaning "characterized by," the term directly translates to "having the qualities of a weasel." Over time, this evolved from a literal descriptor to a primarily figurative one, emphasizing the negative human characteristics of deceit and evasiveness, while also retaining a secondary sense describing a thin or feeble physical appearance.

Structure: weasel (animal) + y (adjective-forming suffix) weasel: From Middle English wesele, from Old English weosule, wesle, of Germanic origin. The animal name forms the core semantic base. y: A productive English suffix from Old English -ig, used to form adjectives meaning "having the quality of" or "characterized by".