late 14c., "expound the meaning of, render clear or explicit," from Old French interpreter "explain; translate" (13c.) and directly from Latin interpretari "explain, expound, understand," from interpres "agent, translator," from inter "between" (see inter-) + second element probably from PIE *per- (5) "to traffic in, sell." Related: Interpreted; interpreting.
early 15c., "hard to understand;" also, of writers, "verbose, using many words;" from Latin diffusus, past participle of diffundere "scatter, pour out," from dis- "apart, in every direction" (see dis-) + fundere "to pour" (from nasalized form of PIE root *gheu- "to pour"). Meaning "widely spread or diffused, scattered" is from late 15c.
[D]istinctly, in the sense really quite, is the badge of the superior person indulgently recognizing unexpected merit in something that we are to understand is not quite worthy of his notice. [Fowler]
early 15c., opake, "dark, shaded, unlit" (a sense now obsolete), from Latin opacus "shaded, in the shade, shady, dark, darkened, obscure," of unknown origin. Spelling influenced after c. 1650 by French opaque (c. 1500), from the Latin. Meaning "impervious to the rays of light" is from 1640s. Figurative sense of "obscure, hard to understand" is from 1761. Related: Opaquely; opaqueness.
c. 1300, conninge, "knowledge, understanding, information, learning," a sense now obsolete, verbal noun from connen, cunnen "to have ability or capacity," from Old English cunnan (see can v.1). By mid-14c. as "ability to understand, intelligence; wisdom, prudence;" sense of "cleverness, shrewdness, practical skill in a secret or crafty manner" is by late 14c.