1. The ordinal number of one million in counting order
   "She was the millionth visitor to the museum"

1. Position 1,000,000 in a countable series of things
   "The millionth visitor to the museum won a lifetime membership"
    
2. One part in a million equal parts
   "One-millionth of Earth's atmosphere is made up of neon";
   - one-millionth

Derived forms: millionths

See also: ordinal

Type of: common fraction, rank, simple fraction, vulgar fraction [Brit]

Encyclopedia: Millionth