The adjective serene means calm, peaceful, or tranquil. It is most commonly used to describe people who display a notably unruffled manner, or natural surroundings that are fair and calm. When applied to people, serene suggests dignity, composure, and graciousness. When applied to nature, it suggests mellowness. Unlike peaceful, serene is not used to describe relations, as between nations, or processes, such as transitions of power. In fact, serene, when not describing an individual's expression or demeanor, is more likely to turn up in descriptions of settings where people are scarce!

Someone who is intrepid stays their course regardless of obstacles that arise. This bold adjective is a close synonym for fearless, but intrepid suggests a degree more resolve and daring. Adventurers, explorers, and travelers are all commonly described as intrepid; reporters, too, though not scaling mountains and traversing seas, are often described as intrepid, surmounting obstacles of a different variety. The phrase intrepid soul is used to refer to an individual who dares to do something to the surprise, delight, or admiration of others.

The verb invigorate is bursting with life! It means “to give vigor to” or “to fill with life and energy.” This animated term is similar to energize, but invigorate, drawing on vigor “vitality,” emphasizes healthy physical or mental energy or power. A brisk walk in mountain air will invigorate your senses; a fascinating conversation will invigorate your mind; and, applied a little more broadly, actions taken by a governing body, such as a city government, might invigorate a local economy.

The verb embroil is used to talk about involvements or entanglements of a particularly contentious or messy nature. If a person is embroiled in controversy, they are at the center of a bitter dispute or are deeply involved in a complex situation marked by discord and hostility. The more general verb involve is often used to talk about participation in something embarrassing or troublesome, but it does not convey the same degree of complication or strife.

Something that is harmful causes or is capable of causing harm (no surprises there!). Something that is pernicious causes insidious harm or even ruin. This sneaky adjective describes things that are both highly destructive and not easy to detect—often because they develop or spread gradually or under the radar. The influence of a person or entity might be described as pernicious if it puts people or things in peril. Similarly, a pernicious myth is one that impairs understanding to the point of causing harm.

An inclination is a liking or preference for something. The synonym penchant is more pronounced and enduring: a penchant is a strong inclination, taste, or liking for something. Penchant is more likely to be used in reference to broad preferences that shape behavior over time. For instance, if a person has a penchant for secrecy, it means they tend toward secrecy not just in an isolated circumstance, but in their conduct more generally. Inclination, on the other hand, may be used to refer to a circumstantial preference: the employee’s inclination was to stay working on the project he started, rather than switch to something new.

The noun fettle is a somewhat old-fashioned way to refer to a person’s physical state or frame of mind. It’s almost always used in the positive with the descriptor fine: a person who is in fine fettle is feeling good and maybe even looking good, too. If you go looking for it, you may spot fettle in other sunny combinations, such as good fettle, excellent fettle, high fettle, and better fettle. Contrast that with the noun condition, which is indeed used to refer to a person’s state of health, but, in those uses, is more likely to be found alongside descriptors such as critical or poor.