I used to own a copy of The meaning of Liff. On the cover there was a large orange sticker which said This book will change your life When you looked at the meaning of the word Liff it said (approximately as this is from memory)
Liff:
Any book whose contents are belied by its cover, for example a book which has an orange sticker on the cover saying This book will change your life but which is actually about nonexistent words
I gave the book to an acquaintance and never saw it again. A few years later I bought another copy, a newer edition, but it didn't have the sticker on it. In the new edition the meaning of Liff had changed. Now it meant
Liff:
Any common experience for which there is not yet a word
I imagine that the cost of placing an orange sticker on the cover was too high for the publishers and they had changed the meaning to make the sticker redundant.

The book was written while the authors were on holiday. The holiday was supposed to be a working holiday during which they would thrash out an outline for one of the hitch-hiker sequels, but Douglas Adams didn't feel like working on the project. They had a road map of Britain with them and were inspired by some strange place names.

Although it has been many years since I have read the book a few of the names/definitions remain with me.

The sequel was called The Deeper Meaning of Liff.