Walk:  An even gait of four beats, with the feet striking the ground in sequence.  There is little elevation of the feet.  The American Saddle Horse and the Tennessee Walking Horse exhibit the running walk, which is a walking gait, but much faster and with a much more extended stride.

Wall:  Side of hoof.

Warm-blood:  Distinguishes those breeds in Germany, which are founded on native mares crossed with Thoroughbreds or Arabs, or with the blood of these in their pedigrees.  The different warm-blood breeds are just as carefully bred as any famous Thoroughbred line and they are therefore considered to be pure-bred.  (It is interesting to note that this was published in London in 1963; today it would probably be acknowledged that all of the above is still true, except that it would now distinguish breeds around the world, and especially across the continent of Europe, and not Germany alone.)

Weanling:  Foals who are between six and twelve months old, or any foal that has been weaned (which usually occurs at about five to six months of age).  Most horses are removed from their mothers (weaned) at six months.  At twelve months of age they are referred to as yearlings.

Welsh Pony:  A lovely, hardy breed of pony that originated in Wales (a small country next to England).

Whicker:  Similar to nicker.

Whipper-in:  In hunting, a person whose duty on the hunt is to keep the pack together.

Withers:  The highest part of the ridge of the back between the shoulder blades, to which point the "shoulder height" of a four-footed animal is measured.  From the Anglo-Saxon wither, meaning against, as in resisting the strain in pulling a load.