BILLIONTH /ˈbɪl.i.ənθ/ ► audio Scrabble 14 Words With Friends 17 Definition adjective the ordinal number of one billion in counting order. noun position 1,000,000,000 in a countable series of things. noun one part in a billion equal parts. — synonyms: one-billionth See all 85 words you can make from BILLIONTH → 9-letter words Words starting with B Words ending with H ← Unscramble different letters