It occurs more often in writing than in conversation. You only use it when you realize that you have actually made an pun, accidentally, but don't want to rewrite the sentence. Sometimes it is used because the pun is so bad that the writer wants you to know that it is not a failed attempt at humor. Here are some examples of actual use: "...legends of a rich Spanish mine have touched off many a vain (no pun intended) search." A "vain search" means an unsuccessful search (and carries the idea that search was unlikely to be successful." A rich deposit of minerals in the ground is a "vein," a completely different word with the same pronunciation. They were search for a vein. The unintended pun is "a vein search," which wouldn't be a good pun because "vein search" is an unnatural word combination. A news story about Hurricane Florence quotes an emergency room director as saying "Once we get isolated we expect to see more. No pun intended, it's a fluid situation." A "fluid situation" means an unpredictable situation that's changing rapidly. In this case, the problem is river flooding caused by a hurricane, and river water is a fluid, so the pun is that it is a literally "fluid situation," a situation involving fluid. Just to make things more confusing, sometimes people will say "no pun intended" when it really is intended. For example, they may say this if the pun is a terrible insult to somebody. Everybody knows the pun is intended, but nobody can prove it, so nobody can object to it.

"The lecture lasted an eternity" means exactly the same thing as "the lecture lasted forever." Both of them are exaggerated ways of saying for "I thought it would never stop" or "It went on much too long." The word "eternity" is a grand word, found in discussions of religion and philosophy. That makes it an even greater overstatement than saying it lasted "forever." Here are some similar pairs of a lesser and a greater exaggeration: 1a: "I'd go anywhere to be with her." b: "I'd travel to the ends of the universe to be with her." 2a: "I'd give a thousand dollars to see 'Hamilton.'" b: "I'd give my right arm to see 'Hamilton.'" 3a: "That will never happen." b: "That will happen when Hell freezes over."

A pun means when you say something, (sometimes by accident), that has or could have another meaning. And coincidentally the two things may have a connection. A pun is a joke of double meanings. "no pun intended" is when you accidentally make a pun by mistakes, it means sorry I did not mean to make a joke. yes an eternity is an extremely long time and you can say that for a lecture. An eternity also means time that never ends. "you will be dead for an eternity" or "you will be dead for a long time" are phrases you will hear they are interchangeable. https://dictionary.cambridge.org/dictionary/english/eternity

1. A pun is a play on words, they are normally not that funny and are often based on words that sound similar. Time and thyme (an herb), for example. No pun intended is something people usually say to draw attention to a pun, although it technically means that they made the pun by accident. So, while cooking, I could tell someone that I have a lot of thyme on my hands, no pun intended (or I can say pun intended if the pun was intentional and planned). Since thyme is an herb, this can literally be true. However, since thyme is pronounced the same as time, there is no way for the speaker to know that I'm not using the expression "time on my hands" unless they are looking at my hands. Likewise, there is a common pun that says that people who wear two watches (which by the way looks quite ridiculous) are trying to have more time on their hands. Likewise, "to raise the roof" is a dance move sometimes used at parties. However, it can also literally mean to raise a roof during construction. To say someone's days are numbered means they don't have long left with whatever it is that they are doing. It can also mean that the days are literally numbered, like in a calendar. Therefore, some other examples of puns include... How do construction workers party? They raise the roof. Every calendar's days are numbered. 2. Yes it is. However, an "eternity" instead of "a long time" is more dramatic, so you may accused of whining/being over-dramatic if you use it too much. Every once and a while though, it can work to get your point across. You can also say something is taking eons and that will get the same idea across.

Pun means paronomasia, synonymy. “sole” and “soul.” Both sound the same, though they have different meanings, creating comic effect. They are called homophonic paronomasia. For more information , review: https://literarydevices.net/paronomasia/