Property relativizing determiner / unary quantifier constructor. {kai'i} introduces a predicate whose first argument slot becomes filled by the property made by taking the bridi in which this {kai'i} appears and putting {ce'u} into the argument slot in which this {kai'i} argument was located. Put formally, "kai'i brodi cu brodu" = "lo ka ce'u brodu cu brodi". Additionally, a {kai'i} term has a rightward logical scope, like quantifiers and adverbials.
x1 is a rodent [can be a member of eutherian mammal Rodentia; semantic broadening might subjectively generalize the concept somewhat] of subtaxon/type/genus/species/breed/variety x2.