In Burns's JOHN ANDERSON MY JO he says "Blessings on your frosty pow" meaning white (wintry) haired head. A friend of mine always sang this verse, ending, "Ya baldy heided bastard"!!
The other definition given for pow is pate i.e. head.
Coming from Paisley some years ago, the word pow was commonly used for head. Sadly, words my father used are no longer used by Scots. Cheers, Jim mcLean