Usborne First Illustrated Science Dictionary

From the back of the book:

Starting at the very beginning with observations of the world around us, this book gently and reliably guides children and parents through the essential science concepts needed in the first few years of school. Readers can use it as a dip-in dictionary or work through by subject to build up knowledge and skills step-by-step.

• Clear definitions of over 350 key terms and concepts

• Hundreds of bright illustrations and useful examples

• Links to the internet's best interactive websites offering science puzzles, games and experiments at this level