The word "庞然大物" is formed by sequentially combining four characters: "庞" meaning huge or vast, "然" which functions as an adjectival suffix denoting a state or manner, "大" meaning big or large, and "物" meaning thing or creature. The phrase structurally pairs "庞然" (gigantic in appearance) with "大物" (large object) to create a compound term that literally translates to "a huge thing" or "gigantic creature".