... the opposite of eloquent?
It's pauciloquent "Uttering few words; brief in speech."
For more '-quents', see this extensive list. You'll find a lot of educated sounding alternatives to lie and blather. E.g.
falsiloquence - deceitful speech
flexiloquent - speaking ambiguously or using words of doubtful meaning
inaniloquent - prone to foolish or empty babbling
mendaciloquence - lying speech
Also good to know:
sialoquent - spitting greatly while speaking
But the best is, nobody will have any idea what you are talking about. Eloquent or not.
See also: Did you know