Proof, a.
 1. Used in proving or testing; as, a proof load, or proof charge.
 2. Firm or successful in resisting; as, proof against harm; waterproof; bombproof.
 I . . . have found thee
 Proof against all temptation.   --Milton.
    This was a good, stout proof article of faith.   --Burke.
 3. Being of a certain standard as to strength; -- said of alcoholic liquors.
 Proof charge Firearms, a charge of powder and ball, greater than the service charge, fired in an arm, as a gun or cannon, to test its strength.
 Proof impression. See under Impression.
 Proof load Engin., the greatest load than can be applied to a piece, as a beam, column, etc., without straining the piece beyond the elastic limit.
 Proof sheet. See Proof, n., 5.
 Proof spirit Chem., a strong distilled liquor, or mixture of alcohol and water, containing not less than a standard amount of alcohol. In the United States “proof spirit is defined by law to be that mixture of alcohol and water which contains one half of its volume of alcohol, the alcohol when at a temperature of 60° Fahrenheit being of specific gravity 0.7939 referred to water at its maximum density as unity. Proof spirit has at 60° Fahrenheit a specific gravity of 0.93353, 100 parts by volume of the same consisting of 50 parts of absolute alcohol and 53.71 parts of water,” the apparent excess of water being due to contraction of the liquids on mixture. In England proof spirit is defined by Act 58, George III., to be such as shall at a temperature of 51° Fahrenheit weigh exactly the part of an equal measure of distilled water. This contains 49.3 per cent by weight, or 57.09 by volume, of alcohol. Stronger spirits, as those of about 60, 70, and 80 per cent of alcohol, are sometimes called second, third, and fourth proof spirits respectively.
 Proof staff, a straight-edge used by millers to test the flatness of a stone.
 Proof stick Sugar Manuf., a rod in the side of a vacuum pan, for testing the consistency of the sirup.
 Proof text, a passage of Scripture used to prove a doctrine.

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From: Webster's Revised Unabridged Dictionary (1913)

 Im·pres·sion n.
 1. The act of impressing, or the state of being impressed; the communication of a stamp, mold, style, or character, by external force or by influence.
 2. That which is impressed; stamp; mark; indentation; sensible result of an influence exerted from without.
    The stamp and clear impression of good sense.   --Cowper.
    To shelter us from impressions of weather, we must spin, we must weave, we must build.   --Barrow.
 3. That which impresses, or exercises an effect, action, or agency; appearance; phenomenon. [Obs.]
    Portentous blaze of comets and impressions in the air.   --Milton.
    A fiery impression falling from out of Heaven.   --Holland.
 4. Influence or effect on the senses or the intellect hence, interest, concern.
    His words impression left.   --Milton.
    Such terrible impression made the dream.   --Shak.
 I have a father's dear impression,
 And wish, before I fall into my grave,
 That I might see her married.   --Ford.
 5. An indistinct notion, remembrance, or belief.
 6. Impressiveness; emphasis of delivery.
    Which must be read with an impression.   --Milton.
 7. Print. The pressure of the type on the paper, or the result of such pressure, as regards its appearance; as, a heavy impression; a clear, or a poor, impression; also, a single copy as the result of printing, or the whole edition printed at a given time; as, a copy from the fifth impression.
    Ten impressions which his books have had.   --Dryden.
 8. In painting, the first coat of color, as the priming in house painting and the like. [R.]
 9. Engraving A print on paper from a wood block, metal plate, or the like.
 Proof impression, one of the early impressions taken from an engraving, before the plate or block is worn.

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