A word maniac or someone who has seizures about words; a verbivore, a logophile.

As Charles H. Elster, in his There’s a Word for It! writes: “The logoleptic person can lose verbal control in various ways—by going gaga over a pyrotechnic display of logodaedaly, by participating in a logomachy over some obscure point of grammar or etymology, or by being rendered senseless by a logographer’s logorrhea.” (page 199)