tu ‧ ber /ˈtjuːbə $ ˈtuːbər/ BrE AmE noun [countable]
[ Date: 1600-1700 ; Language: Latin ; Origin: 'lump, tuber, truffle' ]
a round swollen part on the stem of some plants, such as the potato, that grows below the ground and from which new plants grow
—tuberous adjective