The Oxford Companion to the English Language
by McArthur and McArthur
This book is extraordinary in the breadth and depth of the information it
contains. It covers grammar, syntax, linguistics, speech etc etc. It
addresses English as it is used and spoken in all the major populations and the
influence of other languages on English. It contains more than 3,500 entries.
As an aid in understanding English grammar, it is wonderful in its clarity.