Copious, a.
Etymology: [L. copiosus, fr. copia abundance: cf. F. copieux. See Copy, Opulent.]
Large in quantity or amount; plentiful; abundant; fruitful. Kindly pours its copious treasures forth. Thomson. Hail, Son of God, Savior of men! thy name Shall be the copious matter of my song. Milton.
Syn. -- Ample; abundant; plentiful; plenteous; rich; full; exuberant; overflowing; full. See Ample.
Shades of meaning
Fernald has no entry of its own for copious; he lists it under plentiful.
Where he writes about it:
We may also say a copious rain; but copious can be applied to thought, language, etc., where plentiful can not well be used. — from plentiful
Neither affluent, copious, nor plentiful can be used of time or space; a field is sometimes called plentiful, not with reference to its extent, but to its productiveness. — from plentiful