When my son was younger, we were concerned about his language. He was a preemie, and preemies have a higher likelihood of learning issues. We are watching him, just in case. When Zane was around fifteen months, he got sick, and the few words he knew went away. We were concerned about it, enough to take him to see someone about it. Once he hit the daycare, his language took off running, and he's never looked back. Since then, I have had fun listening to him acquire words and begin to use them in sentences. He's got a hellacious auditory memory--he seems to remember songs after only one hearing, and he can recite almost verbatim what he hears other people saying(hence my concern about profanity!). He certainly has been exposed to an expansive vocabulary.
Zane isn't waiting for us to tell him words, however. He's made a few of them up all on his own. It took my husband and I a little while to catch on. We are a bit slow. But once we realized that our child was playing with language, that he was creating his own version, we couldn't be prouder. He seems to be fond of onomatopoeia. When a video game character causes an explosion of some sort, Zane says that the character got "boomed" up. When a character on the show Ninjago gets attacked with a sword, Zane says that he was "shinged", which is the sound effect that the sword makes when it is pulled from the scabbard. Zane says "last day" instead of "yesterday", which is our clue that he hasn't quite got the full concept of elapsed time. Lots of things have happened "last day" in Zaneworld!
We have tried to expose Zane to as many words as we can, and we will continue to do that. As long as he's interested in what we have to teach him, we will keep trying. My husband always tells Zane the definitions of the words he uses around Zane, which is better than telling him to "look it up." I have been tempted to ask Zane what he thinks the word means
based on how it was used, but I am not sure that it is developmentally
appropriate. I do wait for Zane to ask me about the word, because I know that if he asks me about the word, he is attending. But the words sink in either way, and that is the point. The vocabulary expands, reading skills improve, and teachers write nice notes home for that sort of stuff.