the word 'squirrelly' is a modern english formation that directly appends the adjectival suffix '-ly' to the noun 'squirrel'. the noun 'squirrel' itself has a long history, originating from the ancient greek 'σκίουρος' (skíouros), a compound of 'σκιά' (skiá, "shadow") and 'οὐρά' (ourá, "tail"), literally describing the animal's bushy tail that often curves over its back like a shadow. the characteristic behavior of squirrels—being quick, fidgety, and erratic—became the metaphorical basis for the adjective. thus, 'squirrelly' evolved from a literal descriptor of an animal to an abstract term describing human behavior that is nervous, restless, or eccentrically unpredictable, capturing the essence of the creature's animated movements.

Structure: squirrel + ly squirrel (from middle english 'squirel', from old french 'esquireul', from latin 'sciurus', from ancient greek 'σκίουρος' (skíouros), meaning "shadow-tailed"). ly (from old english '-līc', an adjective-forming suffix meaning "having the qualities of").