A childhood belief about hymns

I used to believe that in the song "Deck The Halls With Boughs Of Holly", "deck" was short for "decorate". It didn't confuse the meaning of that line too much. I'd say back then I was doing well to come that close to getting the meaning of the first line, considering how then I would have been totally clueless about the meaning of other lines, like "Don we now our gay apparrel". And I did wonder what the heck a troll was doing in a Christmas song, the only kind of troll I knew of at the time being a scary creature that lived under a bridge. Although the first line seemed clear, I must have had a somewhat confused time later learning the general meaning of "deck", though.