Sometimes you might hear the phrase, tyranny of the dictionary Is there a way to express succinctly just what that means?
Dictionaries have both descriptive and prescriptive functions, and depending on the philosophy of the editors, different dictionaries may tend to promote one or the other. Most dictionaries today aim to be descriptive, but by their very existence cannot help but be prescriptive as well.
The descriptive function of a dictionary is to describe the language as it exists: what language users say or write, and what those language users mean when they say/write it.
The prescriptive function of a dictionary is norm-setting: once the words of a language are described in the dictionary, it starts to become the standard, possibly stifling innovations in the way words are used. So for example, parents tell their children to go look a word up in the dictionary rather than just telling the child the meaning of the word as the parent understands it. People playing scrabble look up strings of letters in the dictionary to see if they are, in fact, considered words. Writers consult the dictionary to see if, according to the dictionary, they can use a word in a particular way.
So "tyranny of the dictionary" is used as a cute way to describe the prescriptive function of a dictionary, usually by someone who has been caught using a word in a nonstandard (or "wrong" depending on the situation and how you look at it) way.
It is also a play on words with "tyranny of the majority" which is widely used, and has been widely used for a long time in discussions of democracy. So that definitely gives it a boost in usage.
I haven't heard this phrase, but I think I get what it means. A tyrant is a "ruler who uses power oppressively or unjustly."
When you rely on dictionary definitions exclusively, you leave no room for informal, colloquial and regional uses which may not appear in a dictionary. Language moves and changes faster and more subtly than any dictionary can keep up with. Just because something isn't in the dictionary doesn't mean that its use is somehow "incorrect." Have a look at Zairja's link to prescriptivism in the comments.
However, a dictionary can be a useful tool. I use my various dictionaries every day. I even used one in this answer!