Turn off/switch off. In the context of turning off a machine or piece of equipment, these mean the same thing. Interestingly, though, you can use "turn off" (getting turned off, it turns me off, a turn-off) to mean losing your interest or excitement with something or someone. And you can use "switch off" to mean that you're no longer thinking or emoting about a thing ("after an hour of his nagging I just switched off and stopped listening.") Silent/silenced. Something that is making noise can be silenced by stopping the noise. Something that is silent might be that way because it has never made noise, or because it has been silenced. Pretty good/very good. Pretty good means "somewhat good", "fairly good", "some level of good between average and above-average". Very good means "well above averagely good". :) The other pairs mean pretty much the same thing as one another. There are some slight subtle differences between them, but nothing major. For example, kidding refers to speech, but messing can refer to either action or speech.