We call such a response form a neologism. The word “smog” is a good example of a neologism. Presumably the response was first emitted as a result of a strong tendency to say both “fog” and “smoke.” Because both smoke and fog occur together as a stimulus situation, and because there was not already some response form appropriate in this combination of stimulus features, the response “smog” was reinforced since it provided useful information to the speaker. A word is not really a neologism until it has been emitted and reinforced. “Sexting” is another, more recent example of a neologism.