Both words describe something that does not take a direct or straight course from point A to point B. You might take an indirect route home in order to enjoy new sights or to avoid traffic. An indirect route is not necessarily circuitous, but it could be if it’s particularly or unnecessarily complex, lengthy, or roundabout. A circuitous route, road, journey, or process may be twisty and windy or make a circular course to reach the destination. The word can be neutral or have a negative connotation. A circuitous argument, for example, does not get straight to the point and rambles or meanders.

Both words suggest the use of language that is ineffective because it is unoriginal and overused.  A cliché is an expression or saying that has been used so much that it has lost any originality, interest, or impact it might have once had. The expression “white as snow” is a cliché. “Everything happens for a reason” is both a cliché and a platitude. Platitudes are flat, overused remarks, especially moralizing ones offered or spouted to people who are looking for hope, consolation, or just an explanation. As a response to serious civil unrest, “Let us celebrate our differences” would be an empty platitude.

Both words describe beliefs, opinions, or decisions that are strong and unchanging. Someone who has a firm belief in the importance of education is unlikely to change their mind. The word firm has a generally positive connotation—think of muscles, apples, and mattresses, but on the hardness scale it’s less than hard. Adamant, on the other hand, comes from the name of a legendarily hard stone. Adamant opposition and adamant belief are resolute, insistent, even immovable stances that will not give way despite urgings or appeals. When firmness reaches this degree, adamant is a strong synonym for firm. Both words can be used of a person: adamant about the curfew, and their associated words are very similar. Adamant can have a negative connotation and suggest rigidity if sticking to one’s guns becomes more important than the consequences.