Morigerous

Meaning: obedient, compliant, obsequious. 

Usefulness: 1 (It's a word that seems to lend itself to insult: I can imagine calling someone morigerous in a hissed aside, with utmost insouciance, or while yelling and banging on the table. Morigerating and morigerousness - both in the OED - are lovely to say, but seem to come out with a snarl.)

Logofascination: 1 (Morigerate, the verb form, has a citation from 1623 and then one from 1936. How does a 17th century term amuse itself for 314 years? Etymologically, loosely related to morals.)

Haplography

Meaning: writing one letter or word when you should write two - leter instead of letter, or The, when you meant The The. 

Usefulness: 1 (Who knew typos were so specific? Here's to the next level of pedantry.)

Logofascination: 1 (hapolography has nothing to do with mishaps, as I wrongly thought. Haplo means single or simple, whereas in mishap the hap means good luck, fortune, chance, - and, yes, eventually happy - and it's the mis- that indicates that things have gone awry. In case you were wondering, when you write two letters or words instead of one, it's dittography; the the rather than the.)