Synonyms for One:

adj.

•certain (adjective)
several.
•individual (adjective)
different, lone, odd, only, particular, peculiar, precise, separate, singular, sole, solitary, special, specific, uncommon, unique.
•single (adjective)
different, especial, individual, odd, peculiar, precise, separate, singular, sole, solitary, special, specific, uncommon, unique, unusual.
•united (adjective)
unified.

n.

alcohol, aperitif, belt, booze, chaser, cup, double, dram, drink. billion, cardinal number, crore, eight, eighteen, eighty, eleven, fifteen, fifty, first and last, five, include, lone, only, particular, separate, singular, sole, solitary, unique.

v.

•unified (verb)
bound, common, complete, entire, several, unified, united, whole.

Other synonyms:

only, sole, unique. singular. lone, particular. solitary. •Other relevant words:
alcohol, aperitif, belt, billion, booze, bound, cardinal number, chaser, common, complete, crore, cup, different, double, dram, drink, eight, eighteen, eighty, eleven, entire, especial, fifteen, fifty, first and last, five, include, individual, lone, odd, only, particular, peculiar, precise, separate, several, singular, sole, solitary, special, specific, uncommon, unified, unique, united, unusual, whole.

Usage examples for one

1. I don't know but one – Flowing Gold by Rex Beach

2. One day he told me what was on his mind. – Servants of the Guns by Jeffery E. Jeffery

3. I got one too! – Somewhere in Red Gap by Harry Leon Wilson