Something described as Byzantine (or Byzantine) is very complicated, secret, and hard to understand. In its most literal (and always capitalized) sense, Byzantine describes that which is "of, relating to, or characteristic of the ancient city of Byzantium."

// The company's byzantine accounting practices have gotten it into trouble with the government.

// Works of Byzantine art filled the gallery's walls.

Clement is a formal word used to describe weather that is mild, or in other words, neither too hot nor too cold. Clement is also sometimes used to describe someone who is inclined to be merciful or lenient, as in “a clement judge.”

// Although she loves visiting the northeast, Sue prefers to live in places with a more clement climate, without heavy snows or high heating bills.

To lollygag is to spend time doing things that are not useful or serious, or in other words, to fool around and waste time.

// Stop lollygagging and get to work!

// The player was kicked off the team for lollygagging during practice.

Propinquity is a formal word that typically refers to nearness in place or time, making it a synonym of proximity. It can also be used as a synonym of kinship to refer to the state of being related to others by blood.

// The geographical propinquity of these ancient cultures explains many of the architectural similarities.

Fallacious is a formal word that typically describes something, such as an argument or assumption, that is false or inaccurate and that tends to mislead or deceive others. // The notion that disease is caused by malign spirits was known to be fallacious long before the advent of germ theory.

Jeremiad refers to a long cautionary or angry rant about something. It can also refer to a similarly prolonged lamentation, or expression of great sorrow or deep sadness.

// His jeremiad about trivial problems with the campsite didn’t go over well with his friends.

In general contexts, something that ossifies becomes hardened or conventional and opposed to change. In medical contexts, something that ossifies (such as cartilage) forms or is transformed into bone.

// I asked if she'd reconsider her position, but her opinions on the matter have clearly ossified.