Pleonasm, ( n.
Etymology: [L. pleonasmus, Gr. Full, a., and cf. Poly-, Plus.]
(Rhet.)
Redundancy of language in speaking or writing; the use of more words than are necessary to express the idea; as, I saw it with my own eyes.
Shades of meaning
Fernald has no entry of its own for pleonasm; he lists it under circumlocution.
Where he writes about it:
Pleonasm is the expression of an idea already plainly implied; tautology is the restatement in other words of an idea already stated, or a useless repetition of a word or words. — from circumlocution
Pleonasm may add emphasis; tautology is always a fault. — from circumlocution
"I saw it with my eyes" is a pleonasm; "all the members agreed unanimously" is tautology. — from circumlocution