While words such doublet and triplet may be in common use, there are many additional terms to specify higher multiples of items. Here is a summary of the proper terms for 2-15 items of a kind.

2 - doublet
3 - triplet
4 - quadruplet
5 - quintuplet
6 - sextuplet
7 - septuplet
8 - octuplet
9 - nonuplet
10 - decaplet
11 - undecaplet
12 - duodecaplet
13 - tridecaplets
14 - quadecaplets
15 - quindecaplet

Information summarized from data available at: »mypage.direct.ca/c/csams ··· les.html