It’s been said that a mind is a terrible thing to waste! To waste something can be to fail to use it, or to consume, spend, or employ it uselessly or without adequate return. Waste may be used with physical objects or with something more abstract, such as time, effort, or even one’s mind. When seeking a verb that captures an intentionally reckless use of one’s resources (including monetary), squander may be more apt. Squander means to spend or use (money, time, etc.) wastefully or extravagantly, and suggests willfully foolish expenditure, as in, “Instead of honoring his parents’ legacy, he squandered their money on parties and fancy cars.”

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.