These words are closely related in meaning to each other and to such adjectives as merry, convivial, gay, mirthful, jocund, jocose, gleeful, happy, cheerful, blithe, sportive, sprightly, airy, light-hearted, lively, vivacious, and frolicsome. Jolly especially denotes a natural, good-humored, expansive gaiety of mood or disposition: "We had a jolly crowd at the last party." "For he's a jolly good fellow." Jocular suggests "joking," "jesting," "waggish," "facetious": "Many jocular remarks were addressed to the bridegroom." "Being in a jocular mood, the speaker told several amusing stories." Jovial suggests a hearty, earthy, joyous humor, a spirit of good-fellowship: "He was a jovial host who made everyone feel welcome."
Dictionary of problem words and expressions. Harry Shaw. 1975.