Merriam-Webster's Collegiate® Dictionary, 11th Edition
BUTTERFLY
I. noun
Usage: often attributive Date: before 12th century any of numerous slender-bodied diurnal lepidopteran insects including one superfamily (Papilionoidea) with broad often brightly colored wings and usually another superfamily comprising the skippers, something that resembles or suggests a butterfly, a swimming stroke executed in a prone position by moving both arms in a circular motion while kicking both legs up and down, a feeling of hollowness or queasiness caused especially by emotional or nervous tension or anxious anticipation, a defensive move by a goalie in ice hockey executed by dropping to the knees while spreading the lower legs outward,
II. transitive verb (-flied; -flying)
Date: 1954
to split almost entirely and spread apart