word-forming element meaning "not, opposite of, without" (also im-, il-, ir- by assimilation of -n- with following consonant, a tendency which began in later Latin), from Latin in- "not," cognate with Greek an-, Old English un-, all from PIE root *ne- "not."
In Old French and Middle English often en-, but most of these forms have not survived in Modern English, and the few that do (enemy, for instance) no longer are felt as negative. The rule of thumb in English has been to use in- with obviously Latin elements, un- with native or nativized ones.
1610s, "open to the understanding, not obscure or ambiguous," from French explicite, from Latin explicitus "unobstructed," variant past participle of explicare "unfold, unravel, explain," from ex "out" (see ex-) + plicare "to fold" (from PIE root *plek- "to plait").
As a euphemism for "pornographic" it dates from 1971 (phrases such as sexually explicit are earlier). Related: Explicitness. "Explicitus" was written at the end of medieval books, originally short for explicitus est liber "the book is unrolled."
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Definitions of inexplicit from WordNet
implied though not directly expressed; inherent in the nature of something;