Syllable division derived from spelling — this word is not in the pronouncing dictionary, so no phonetic transcription is shown rather than a guessed one.
mirthful is an adjective meaning "full of or showing high-spirited merriment". It carries 2 recorded senses.
full of or showing high-spirited merriment
“when hearts were young and gay”
“a poet could not but be gay, in such a jocund company”
“the jolly crowd at the reunion”
“jolly old Saint Nick”
“a jovial old gentleman”
“have a merry Christmas”
“peals of merry laughter”
“a mirthful laugh”
arousing or provoking laughter
“an amusing film with a steady stream of pranks and pratfalls”
“an amusing fellow”
“a comic hat”
“a comical look of surprise”
“funny stories that made everybody laugh”
“a very funny writer”
“it would have been laughable if it hadn't hurt so much”
“a mirthful experience”
“risible courtroom antics”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for mirthful come from Princeton University’s WordNet. Commonness is measured against a corpus of everyday English. Full sources and licences.