This article analyses longitudinal diary data from one infant acquiring German to seek a better understanding of the role of onomatopoeia in early language development. Onomatopoeic words (OWs) are traced over time in relation to their corresponding conventional forms (CWs), and an analysis of their phonological transitions is considered in relation to the infant's wider language development. OWs are found to serve as a bootstrapping mechanism on a lexical as well as a phonological level, and a lexical OW "template" is proposed, which is found to support phonological development throughout the infant's output.