The Oxford English dictionary.
The origins of English words : a discursive dictionary of Indo- European roots
Webster's word histories.
A history of the English language
The roots of English : a reader's handbook of word origins
The Cambridge history of the English language.
Reading the OED : one man, one year, 21,730 pages
Mythology by Edith Hamilton
Bulfinch's mythology; the age of fables; The age of chivalry; Legends of Charlemagne.
Early Greek myth : a guide to literary and artistic sources
Greek and Roman mythology