(See also TEST.)

acid test Any crucial or conclusive test to judge value or genuineness; the “real” test. The term is an extension of a chemical test using nitric acid or aqua fortis, as it is sometimes called, to determine the gold content of jewelry. Used literally in 1892 in G. F. Gee’s The Jeweller’s Assistant, the expression was first used in its figurative sense in 1912:

Aunt Sally See VICTIMIZATION.

bench mark A standard or touchstone against which to measure; a criterion or test. A bench mark is literally a surveyor’s arrow-shaped mark indicating a given elevation used as a point of reference in measuring other elevations. According to the OED the name comes from the way a surveyor’s angle-iron forms a bracket or bench to support the leveling-staff when taking a reading. The term was used figuratively as early as 1884 in Science:

landmark decision A verdict issued by a high court (e.g., the Supreme Court) which determines the direction or disposition of a previously untried issue; a precedent-setting ruling. Traditionally, a landmark is a guide for direction in one’s course, or, metaphorically, an event that marks a turning point in history. As an adjective, landmark has come to describe any decision or legislation of such significance that it will serve as a guide or criterion in similar matters in the future.

play in Peoria To be accepted by the common man of “Middle America.” Peoria, a small town in central Illinois, has come to represent traditional, down-to-earth American values, perhaps originally from the experiences of traveling theater troupes in playing to small town audiences. Today the expression is most often heard in the political context; “playing in Peoria” successfully has become the touchstone for determining an idea’s appeal to the American public at large.

Procrustean bed An arbitrary system or standard to which ideas, facts, etc., are forced to conform. In Greek mythology, the robber Procrustes made his victims fit the length of his bed by stretching or amputating their limbs. Thus, to stretch or place on the bed of Procrustes is to produce conformity by violent, irrational means. Figurative use of Procrustean bed dates from the 16th century.

the proof of the pudding is in the eating A proverbial admonition against passing judgment on something without first examining the evidence or facts; often shortened to the proof of the pudding. Another popular proverb conveying basically the same message is the imperative don’t judge a book by its cover.

rule of thumb A rough guide or approximate measurement; a practical criterion or standard. The thumb’s breadth was formerly used in measurements to approximate one inch. Since such reckoning was imprecise and unscientific, rule of thumb has come also to indicate a guideline resulting from instinct rather than from scientific investigation. The phrase has been in figurative use for nearly three centuries.

sounding board A person to whom new concepts and ideas are presented for his reaction or opinion. A sounding board is a structure which reflects sound back to an audience. Its figurative usage was illustrated in Atlantic, as cited by Webster’s Third:

touchstone A criterion or test; a standard or measure. A touchstone is literally a smooth, black, siliceous stone used to test the purity of gold and silver alloys. By rubbing the alloy on the stone and analyzing the color of the streak on the stone, the gold or silver content can be determined. The term was used both literally and figuratively as early as the mid-15th century.

trial balloon Literally, a balloon which is used to test air currents and wind velocity. By extension, a trial balloon is any specific proposal, statement, etc., used to test public reaction by provoking feedback.