The term 'a billion' is used to refer to a very large number, usually 1, 000, 000, 000. The crossword solutions for this term include EON (3 letters), ISLAM (5 letters), INDIA (5 letters), EONS (4 letters), GIGA (4 letters), and AEON (4 letters). EON is an indefinite period of time, while ISLAM is a major world religion. INDIA is a country in South Asia, while EONS is another word for a very long period of time. GIGA is a prefix meaning one billion, and AEON is another word for an indefinitely long period of time.