Noah Webster's New International Dictionary of the English Language

1. (a.) Not pure; not clean; tainted; dirty; foul; filthy; containing something which is unclean or unwholesome; mixed or impregnated extraneous substances; adulterated; as, impure water or air; impure drugs, food, etc.

2. (a.) Defiled by sin or guilt; unholy; unhallowed; -- said of persons or things.

3. (a.) Unchaste; lewd; unclean; obscene; as, impure language or ideas.

4. (a.) Not purified according to the ceremonial law of Moses; unclean.

5. (a.) Not accurate; not idiomatic; as, impure Latin; an impure style.

6. (v. t.) To defile; to pollute.