Deca- is a Greek prefix meaning ten (see Greek numerical prefixes.) The Latin equivalent is deci-.

For the use of this prefix in SI units see Deca

Some examples:

• In calendars a decade is a period of ten years.

• In electromechanical equipment a decade is a group of ten numbers on a switch or indicator, which may represent units, tens, hundreds, etc.

• A Decapod is a ten legged creature. One kind of decapod is the lobster (a kind of arthropod of the order decapoda), another is the cuttlefish (a kind of cephalopod).

• A decagon is a polygon with 10 sides.