The word 'tuber' entered English in the mid-17th century directly from Latin, where tūber signified a bump, swelling, or protuberance. This Latin term is believed to derive from the Proto-Indo-European root teue-, meaning 'to swell', which also gave rise to words like 'thumb' and 'tumour'. The botanical application to describe the swollen, food-storing part of a plant stem or root is a direct metaphorical extension of this core concept of a rounded swelling. Thus, the modern word retains its original sense of a protuberance while being specifically applied in botany and anatomy.

Structure: tub (swelling) + er (noun suffix) - tub: From Latin tūber meaning a lump, swelling, or hump. - er: A common English noun-forming suffix, often indicating an agent or object associated with the root.