This article examines the creation of novel words by two English-speaking male siblings, ages five- and six-years-old, during a fourteen-month period of weekly play sessions. The questions the article addresses are: Did the boys produce novel words? What types of words? Why were these words created? and Did they become a permanent part of the siblings' vocabularies? The authors categorized all novel words as either developmental substitution, word play, redundant duplication, or word gap, depending on how the words functioned in the boys' conversations. In this dyad, novel words functioned primarily as word play and filling a word gap (thereby providing a precise way to convey meaning). The novel words were nearly all nonce formations (isolated occurrences) and were composed mainly of compound words (two- or three-word combinations) and pseudowords (fictitious words). When the boys repeated novel words, they usually did so immediately, i.e. within the same play session. The study suggests that these children spontaneously produced a varied repertoire of novel words to meet and expand the needs of their imaginative or pretend play. The words were created in the moment and arose from the novel concepts and themes of pretend play. Research for this article was funded in part by the University of North Carolina at Greensboro.