Waveringly.
Aerobic
Supercalifragilisticexpialidocious
Terrific (and super) 
Carolers
Manger
Reindeer
Nutcrackers
Gingerbread House
Cranberries
Sherry
Merry
Is there any other Christmassy words with “er” in them?
…or back to A-W
Unnerving
Verve.
Weather
A
Oops! Didn’t realise it was supposed to be in alpha order - Sorry!
Acerbic
Berberis
Cervical
No problem Boot, I do it all the time.
Dervish
1 Like
Effervescent
Fervently.
Geronimo
Heralds.
Interiors
J
Joker
Leader
Merchant