The compound 'three-sixty' is a modern English formation that directly combines two cardinal numbers, 'three' and 'sixty', both of which have ancient Indo-European lineage. Their primary function is to denote the specific quantity 360, a number of historical and practical significance as it represents the total degrees in a full circle. This literal numerical meaning evolved metaphorically in the 20th century, particularly in sports jargon, to describe a complete aerial rotation. From there, the term was further abstracted into general usage to signify a comprehensive turnaround or complete reversal in any context, completing its journey from a simple arithmetic sum to a vivid idiomatic expression.

Structure: three (quantity) + sixty (quantity) - three: From Old English þrīe, of Germanic origin; related to Dutch drie and German drei, from an Indo-European root shared by Latin tres and Greek treis. Functions as a cardinal number. - sixty: From Old English sixtig, from the Germanic base of six + the suffix -tig (meaning 'group of ten'). Functions as a cardinal number.