The compound adjective 'three-round' is a modern formation built from two ancient roots. The first element, 'three', descends from the Proto-Indo-European numeral treies-, a concept so fundamental it is preserved across most descendant languages. The second element, 'round', traces back to the Latin rota (wheel), evoking the image of a completed cycle or revolution. In competitive or procedural contexts, a 'round' came to signify a distinct stage within a larger sequence. Thus, 'three-round' logically denotes an event or process structured into three complete cycles or phases, directly linking the ancient sense of a circular revolution to the modern abstract meaning of a procedural stage.

Structure: three (number) + round (stage) - 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 numerical quantifier. - round: From Old French rond, from Latin rotundus 'round', from rota 'wheel'. In this compound, it functions as a noun meaning a stage, session, or bout of an activity, a sense derived from the concept of a completed cycle.