Adjective
The word is derived from merry
You must wake and call me early, call me early, mother dear To-morrow'll be the happiest time of all the glad New Year, Of all the glad New Year, mother, the maddest, merriest day For Im to be Queen o' the May, mother, I'm to be queen o' the May. Alfred, Lord Tennyson
England was merry England, when Old Christmas brought his sports again. ‘Twas Christmas broach'd the mightiest ale; ‘Twas Christmas told the merriest tale; A Christmas gambol oft could cheer The poor man's heart through half the year. Walter Scott