Adjective
imprimitive (not comparable)
(mathematics) not primitive
Antonym: primitive
The imprimitive maximal subgroups are exactly those of the form Sym(k) wr Sym(n/k) where 2 ≤ k ≤ n/2 is a proper divisor of n and "wr" denotes the wreath product acting imprimitively. Source: Internet
This does not give a well-defined action on primitive triples, since it may take a primitive triple to an imprimitive one. Source: Internet