Which word best describes something that is easily understood and clear?

The word "luculent" is the best choice to describe something that is easily understood and clear. It derives from Latin, meaning "light" or "clear," and in modern usage, it refers specifically to anything that is expressed in a way that is coherent and easily grasped. Thus, when describing a text, a concept, or any form of communication, using "luculent" implies that it possesses clarity and is readily comprehensible to the audience.

In contrast, the other options do not convey the same clarity of understanding. "Officious" describes someone who is excessively eager to offer unwanted help or advice, lacking the connotation of clarity. "Ostensible" refers to something that appears to be one way but may not accurately reflect the underlying reality, which does not imply clarity at all. "Maunder" means to talk in a rambling or incoherent manner, directly opposing the notion of clarity or being easily understood. Therefore, "luculent" stands out as the term that best captures the essence of being clear and comprehensible.