Perspicuous, a.
Etymology: [L. perspicuus, from perspicere to look through. See Perspective.]
1. Capable of being through; transparent; translucent; not opaque. [Obs.] Peacham.
2. Clear to the understanding; capable of being clearly understood; clear in thought or in expression; not obscure or ambiguous; as, a perspicuous writer; perspicuous statements. "The purpose is perspicuous." Shak. -- Per*spic"u*ous*ly, adv. -- Per*spic"u*ous*ness, n.
Shades of meaning
Fernald has no entry of its own for perspicuous; he lists it under clear.
Where he writes about it:
Perspicuous is often equivalent to plain, but plain never wholly loses the meaning of unadorned, so that we can say the style is perspicuous tho highly ornate, when we could not call it at once ornate and plain. — from clear