This dictionary represents a small fragment of what is known of the Celtic language spoken in Lowland Britain from the pre-Roman Iron Age (800 BC - 42 AD) until its displacement by Germanic dialects in the mid first millennium. This book is intended to serve as a foundation upon which a greater understanding and ultimate revival of this language can be based. All forms presented within are based either on first-hand evidence (attested personal, tribal, and place names) or reconstructed based on evidence from later Brythonic (Welsh, Cornish, or Breton) and Proto-Indo-European (PIE). Reconstructable forms lacking a British source (those based purely on Goidelic or Continental dialects) have been excluded.