The word "lengthy" describes something that is long in duration, extent, or size. It often refers to something that takes a considerable amount of time to complete or is more extensive than usual. For example, a lengthy lecture would be a class that goes on for a long time, and a lengthy report would be a document that is quite long in terms of pages or words.
The term "lengthy" originates from the word "length," which comes from the Old English "length," meaning the measurement of something from end to end. The suffix "-y" is often added to adjectives in English to indicate a characteristic or quality. Thus, "lengthy" literally means having a lot of length.