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Lenny 'to dress' means 'to set in place' or 'to set one's self'. On page 25 of my version it says "[...] and dressed his shield and took a spear [...]" So in that case it is 'to set his shield in place'
Chris Macdonnell As Alannah says, to set in place is correct, and in the case of a shield, that's facing away from the knight and therefore towards any opponent or danger. The use of the word DRESS is often of setting yourself to face something or someone. We now say we ADDRESS a problem, or ADDRESS an audience which is similar in meaning. When we dress ourselves in the morning, or wear a dress, that use of dress is rooted in the same thing. A cover which we set on ourselves which faces outward.