Tertiary is an adjective meaning "third" or "third hand". It may refer to:

• The Tertiary period of the geologic timescale
• Tertiaries, members of a Third order (lay folk connected with a Mendicant Order).
• Ternary, the base- numeral system.
• A tertiary consumer in an ecological sense.
• A Tertiary functional group (or usually ion) attached to carbon atom connected to 3 other Carbon atoms in organic chemistry

See also

• Primary
• Secondary
• Quaternary