Logorrhea

logorrhea \ˌlo⋅-gə-ˈrē-ə, ˌlä-\ noun: excessive and often incoherent talkativeness or wordiness

Etymology: New Latin, from Greek logos speech, word, reason + -rrhoia, from rhoia, from rhein to flow

We all know someone afflicted with this terrible malady. Sadly there is often no cure.