Something mutual is held in common or experienced between two parties, as in mutual friends. Similarly, reciprocal indicates a balanced relationship between two or more people, in which an act, thing, or feeling is given in return for another. Unlike mutual, reciprocal also carries the meaning of “matching or equivalent.” So a reciprocal promise may be made to ensure that both parties will maintain confidentiality about a matter. Often used in math, navigation, and grammar, reciprocal has a more technical implication of being one-for-one or the exact opposite or inverse of something, whereas mutual features in the world of finance or insurance when assets are shared (e.g., mutual funds). 

Someone who is jolly is lively or merry. The figure most associated with the adjective jolly may be Jolly Old Saint Nick, or Santa Claus, often depicted belly-laughing with a merry twinkle in his eye. Mirthful, on the other hand, evokes mischievousness rather than the hearty “ho, ho, ho” of jolly. Mirthful, while less common than jolly, may be used to describe one’s mood, smile, or laughter itself, all containing a hint of being entertained by some secret silliness.

Generosity refers to a readiness or liberality in giving, and sometimes to an overall spirit of kindness. Another way to name generous giving, when it involves gifts or money, is with the noun largess. Largess can also refer to the gifts themselves. At the root of largess is the word "large," so one way to think about it is that those who show largess are characterized by the largeness of their contributions, monetary or otherwise. Most commonly, you will see largess used in the public works sense, denoting a sense of superiority or higher rank on the part of the one or ones bestowing it.