Is there a word that describes when you are unable to remember the word you want to say?

You're most likely thinking of lethologica, but you should note that this is a psychological condition, as opposed to the passing frustration we all experience from time to time.

A more accurate term for the tip-of-the-tongue phenomenon is the French presque vu (literally, "almost seen").

The word is dysnomia or aphasia. and it is a memory storage disorder. You brain learns the word and just places it randomly in your memory storage. When you go to recall the word your brain cannot find it right away because it is not where it should be. That is why you usually remember it later that night or the next day, because though you have given up your brain has not and it continues to check your memory for the answer!

No it's not logonamnia. I just found it. It's actually loganamnosis! Yay!

Edit: Word Info, A mania, or obsession, for trying to recall forgotten words or a specific word.