Nonce borrowings in the speech of bilinguals differ from established loanwords in that they are not necessarily recurrent, widespread, or recognized by host language monolinguals. With established loanwords, however, they share the characteristics of morphological and syntactic integration into the host language and consist of single content words or compounds. Furthermore, both types of loanwords differ from intrasentential code-switching — alternate sentence fragments in the two languages, each of which is grammatical by monolingual standards from the standpoints of appropriate function words, morphology, and syntax. In a large corpus of Tamil—English bilingual speech, many words of English origin are found in objects governed by Tamil verbs and vice versa. The equivalence constraint on intrasentential code-switching predicts that no code-switch should occur between verb and object in an SOV/SVO bilingual situation, and hence that objects whose language differs from that of the verb must be borrowed, if only for the nonce. To verify this prediction, we compare quantitatively the distribution across various syntactic contexts of both native Tamil and English—origin complements of Tamil verbs, and find them to be parallel. But the strongest evidence in favor of the nonce borrowing hypothesis comes from an analysis of variable accusative and dative case marking in these complements, in which the English-origin material is shown, morphologically and syntactically, to be virtually indistinguishable from Tamil (nonpronominal) nouns. In addition, we present supporting evidence from the genitive, locative, and other cases and from nonce borrowings from Tamil into these speakers' English.