I don't know of any book that completely answers your question, but there are a few generally helpful books that cover some of the terminology. Some also, however, contain some info on how-to's, which parts will not be of use. My recommendations concerning terminology definitions:
Taylor's Dictionary for Gardeners covers some oft-used terminology. From Amazon:
From everyday gardening terms to essential botanical Latin, this illustrated book is truly a dictionary of horticultural literacy for gardeners of every level of interest and experience. With 2,000 entries and 275 illustrations, Taylor's Dictionary for Gardeners defines and clearly explains the terminology of horticulture, including:The botanical names of common species, or how to read a plant label, Horticultural terms - the difference between genus,species, cultivar, and hybrid, Garden techniques, such as what it means to scarify seeds and distress roots, The anatomy and physiology of plants, including the everyday significance of apical dominance, Historical gardening terms and styles, from ha-ha to bedding out. The book also includes names and descriptions of garden tools and insect pests, brief biographies of famous gardeners, and listings of botanical gardens and institutions in the world of horticulture.
The Kew Plant Glossary: An Illustrated Dictionary of Plant Terms is also a good one, but also contains something of a field guide.
This accessible, comprehensive glossary covers all the descriptive terms for plants that one is likely to encounter in botanical writing, including everything from magazine articles to plant field guides, scientific papers, and monographs. An essential companion, it presents 3,600 botanical terms, accompanied by full definitions and detailed illustrations to aid in identification, all laid out in a clear, easy-to-use fashion. It will be indispensable for plant scientists, conservationists, horticulturists, gardeners, writers, and anyone working with plant descriptions, plant identification keys, floras, or field guides.
The Cambridge Illustrated Glossary of Botanical Terms Is more in-depth, and contains many terms even most avid gardeners don't know.
This beautifully illustrated glossary constitutes an extraordinary collection of the specialist terms used in many botanical works. The book is arranged in two sections: the glossary, which provides clear definitions for over 2400 of the most commonly used botanical and horticultural terms, and illustrations, which can be cross-referenced to the glossary. The illustrations section comprises over 120 large format pages packed with accurate, well labelled line drawings that complement the definitions. The illustrations are grouped according to specific features, allowing quick comparisons of different forms. This outstanding reference will be welcomed by all readers grappling with botanical terms, whether student, professional, or hobbyist.
Plant Identification Terminology: An Illustrated Glossary Covers the terminology useful when one is trying to identify a plant.
Plant identification employs an extensive and complex terminology. Professional botanists often need several years in the field to master this terminology, and it presents a daunting obstacle to the student of botany.
The meaning of most botanical terms, however, is immediately apparent when an illustration is available. That is the purpose of this volume. Plant Identification Terminology provides over nineteen hundred clear illustrations of terms used in plant identification keys and descriptions. It also includes definitions for more than twenty-seven hundred taxonomic terms.
A Dictionary of Botanical Terms Is an older one, but I think a staple.
John Stevens Henslow (1796-1861) was a botanist and geologist. As teacher, mentor and friend to Charles Darwin, it was his introduction that secured for Darwin the post of naturalist on the voyage of the Beagle. While Professor of Botany, Henslow established the Cambridge University Botanic Garden as a resource for teaching and research. Students were encouraged to examine plant specimens carefully, and to record the characteristics of their structures. Henslow would have known how daunting they found the task of becoming proficient with botanical vocabulary, and produced this volume to provide a secure foundation for scientific investigations. This meticulous glossary, originally published as a single volume in 1857 but drawing on contributions he made earlier to issues of The Botanist and Maund's Botanic Garden, is a testament to Henslow's scholarship. It is liberally illustrated with delightful woodcuts that clarify the meaning of selected terms.