Explores how to develop children's understanding of mathematical vocabulary. Presents a lesson in which the class works on the concept of dimension, and issues raised by a discussion of applied linguistics and mathematics education. Discussion was stimulated by advice from the National Numeracy Strategy (NNS) vocabulary book. (KHR)

National Numeracy Strategy (NNS) guidance appears to characterise mathematical language as a set of specialist words with unambiguous definitions, yet analysis of the classroom transcript suggests that at least some mathematical concepts cannot be captured by such definitions. This paper explores the notion of definition within mathematics,…