This paper details the methodology originally used for a cross-sector literature review of formative evaluation in Germany. The study involved an online keyword search using academic databases and Google Search to uncover documents containing and meaningfully discussing formative evaluation as well as alternative forms of this term in German that matched a predefined conceptualization, a process termed here 'semantic iterative keyword sampling' (SIKS). Formative evaluation was recognized from the outset as a polyonym (defined as each of at least four different terms having the same meaning) in German, but the search revealed that German authors use no fewer than 47 terms to refer to this concept -- far more than expected. Formative evaluation appears to be a polyonymous concept even in English. This demonstrates the utility of a more comprehensive and structured approach to online keyword searches for lexically flexible concepts. Educational researchers studying other polyonymous concepts may find SIKS to be useful for collecting more data within not only the target context but also other disciplinary and linguistic domains.