ABSTRACT Linguists today presuppose that for both description/analysis and comparison of languages, there is a substantial set of universal crosslinguistic categories. In the same way, in the grammaticisation of non-European languages, missionaries took the grammatical categories elaborated for Latin as a set of universal crosslinguistic categories. One could assume that they fell into the trap of transferring time-tested terminology from traditional Latin grammar adapting it to the description of a language with rather different structural properties without really capturing its ‘genius’. Even if this assumption may certainly be true to some extent, it does not present the whole picture and it does not do justice to the efforts missionaries made in describing new languages. Therefore, focusing on how missionaries understood and described the Tamil relative clause and relativiser marker, this paper aims to discuss the tension arising in grammatical descriptions between language-particular categories and crosslinguistic conceptual transfer. The paper thus demonstrates how missionaries did not limit their accounts to the transfer of a priori grammatical categories, tailored for Latin and applied to Tamil, but rather how they refined their descriptions through a crosslinguistic conceptual transfer that may be considered the first step towards comparative concepts.