"Learning to read music, and learning its grammar, need not be dull or too much trouble," writes Benjamin Britten in his Foreword to this book. An introduction to the language of music, designed for the amateur musician, An ABC of Music surveys all the musical terms and ideas likely to be met in the beginning stages of learning to play an instrument. A short, practical guide to the essentials of rudiments, harmony, and form, it is capable of being read straight through with pleasure and understanding, but may also be used as a sort of cumulative dictionary, with each definition leading on to the next.
Imogen Clare Holst CBE (12 April 1907 – 9 March 1984) was a British composer, arranger, conductor, teacher, musicologist and festival administrator; and the only child of the composer Gustav Holst.
She is particularly known for her educational work at Dartington Hall in the 1940s, and for her 20 years as joint artistic director of the Aldeburgh Festival.
In addition to composing music, she wrote composer biographies, much educational material and several books on the life and works of her father.
I don't know if I understood more than half of this book, but it looks like a decent and very comprehensive (if short, and rather clipped in its manner) reference for every type of musical term.