In the sparse literature about definitions, most publications are from Academia. However, Nordterm 8 Guide to Terminology by Heidi Suonuuti (ISBN 952-9794-14-2) is a very useful and practical booklet from a practicioner community. Further details can be found at
Nordterm describes itself as follows: "Nordterm is an association of organisations and societies in the Nordic countries which are engaged in terminology work, training and research.". Terminology work, of course, covers much more than definitions, but A Guide to Terminology does contain a fair amount on definitions, and has a very practical focus.
Nordterm 8 contains a very useful set of references, particularly about ISO Standards. It introduces definitions in a section on Concept Analysis, that is also valuable as an overview of ontology - again from a practical perspective. A section dedicated to definitions follows, with systematization in terminology work as a special focus. A valuable high level methodology for terminology work is presented next - again very practical. Deficient definitions are examined next. The following major section is on terms. This, of course, is a specialist topic within terminology, but obviously closely allied to definition work. Finally, there is a summary of the terms used in terminology work (alas without definitions) and their translations in Nordic languages. The whole booklet is 42 pages.
A Guide to Terminology would be valuable just because there is so little literature, and Academia seems to have a mission to avoid any practical contributions. However, the booklet packs a lot into a small volume and is highly informative and will be a help to any practicioner.