The Oxford Dictionary of Word Histories (Oxford Paperback Reference)

This books is a 560 page long paperback dealing with words and their origins and is a must for those interested in such things.

Here are a few random entries:

Bald.

[Middle English]. The likely semantic base of bald is 'white patch', leaking to the archaic English sense 'marked or streaked with white'. The Welsh ceffyl bal provides a comparison, denoting a horse with a white mark on its face. Several Indo-European synonyms of bald show a connection with 'smooth', 'bright', 'shiny' rather than with hairlessness as such.

Flaw

[Middle English]. This is perhaps from old Norse flaga 'slab'. The original sense was a 'flake of snow' and it later came to mean a 'fragment or splinter'. This gave rise in the late 15th century to the sense 'defect or imperfection'.

Seam

[Old English]. Old English seam is of Germanic origin related to the Dutch zoom and the German saum. Use of the word in geology (coal seam) dates from the late 16th century. The word seamstress (also late 16th century) is based on archaic seamster, sempster 'tailor, seamstress', which originally referred to a woman but in Old English was already starting to be applied to a male tailor.

Stimulating and entertaining. Contains very recent words as well as well as established ones.
It's useful to keep to hand to look up words as needed, but it also makes a pleasant read in its own right.
The origin of words is a great aid to understanding.