Ample, a.
Etymology: [F. ample, L. amplus, prob. for ambiplus full on both sides, the last syllable akin to L. plenus full. See Full, and cf. Double.]
Large; great in size, extent, capacity, or bulk; spacious; roomy; widely extended. All the people in that ample house Did to that image bow their humble knees. Spenser.
2. Fully sufficient; abundant; liberal; copious; as, an ample fortune; ample justice.
3. Not contracted of brief; not concise; extended; diffusive; as, an ample narrative. Johnson.
Syn. -- Full; spacious; extensive; wide; capacious; abundant; plentiful; plenteous; copious; bountiful; rich; liberal; munificent. -- Ample, Copious, Abundant, Plenteous. These words agree in representing a thing as large, but under different relations, according to the image which is used. Ample implies largeness, producing a sufficiency or fullness of supply for every want; as, ample stores or resources, ample provision. Copious carries with it the idea of flow, or of collection at a single point; as, a copious supply of materials. "Copious matter of my song." Milton. Abundant and plenteous refer to largeness of quantity; as, abundant stores; plenteous harvests.
Shades of meaning
Fernald has no entry of its own for ample; he lists it under large, plentiful.
Where he writes about it:
That is ample which gives a safe, but not a large, margin beyond a given demand; that is abundant, affluent, bountiful, liberal, plentiful, which is largely in excess of manifest need. — from plentiful
Ample and abundant may be applied to any subject. — from plentiful
We have time enough, means that we can reach our destination without haste, but also without delay; if we have ample time, we may move leisurely, and note what is by the way; if we have abundant time, we may pause to converse with a friend, to view the scenery, or to rest when weary. — from plentiful