Synonyms for Six:

n.

crore, five, eighteen, eighty, eleven, fifteen, eight, fifty, cardinal number, billion. six (noun)
half dozen, half a dozen, hexad, cardinal, sextuplet, sise, 6, sixer, captain hicks, sestet, vi, sextet.
six of something (noun)
hexad, sextet, sextuplet.

Other synonyms:

VI
vi.
Other relevant words:
crore, five, eighteen, eighty, eleven, fifteen, eight, fifty, cardinal number, billion.