-tuple

Concise Oxford English Dictionary © 2008 Oxford University Press:
-tuple /ˈtjuːp(ə)l/

▶combining form chiefly Mathematics forming nouns and adjectives with a preceding algebraic symbol with the sense ‘(an entity or set) consisting of as many parts or elements as indicated by the symbol, such as n-tuple.

– origin from the ending of quintuple, octuple, etc.