1.  litmus test(n = noun.substance) litmus - a coloring material (obtained from lichens) that turns red in acid solutions and blue in alkaline solutions; used as a very rough acid-base indicator;
is a kind of acid-base indicator

2.  litmus test(n = noun.communication) - a test that relies on a single indicator; "her litmus test for good breeding is whether you split infinitives"
is a kind of exam, examination, test

1.  A test to determine acidity or alkalinity, using litmus as an inddicator. [PJC]

2.  A test for a single factor, which has only two outcomes, positive or negative; [PJC]

N  experiment, essay, analysis, screen, trial, tentative method, t=atonnement, verification, probation, experimentum crucis, proof, (demonstration), criterion, diagnostic, test, probe, crucial test, acid test, litmus test, crucible, reagent, check, touchstone, pix, assay, ordeal, ring, litmus paper, curcuma paper, turmeric paper, test tube, analytical instruments, empiricism, rule of thumb, feeler, trial balloon, pilot balloon, messenger balloon, pilot engine, scout, straw to show the wind, speculation, random shot, leap in the dark, analyzer, analyst, assayist, adventurer, experimenter, experimentist, experimentalist, scientist, engineer, technician, subject, experimentee, guinea pig, experimental animal, protocol, experimental method, blind experiment, double-blind experiment, controlled experiment, poll, survey, opinion poll, epidemiological survey, retrospective analysis, retrospective survey, prospective survey, prospective analysis, statistical analysis, literature search, library research, tryout, audition, discovery, measurement, evidence, deduction, induction, abduction, experimental, empirical, probative, probatory, probationary, provisional, analytic, docimastic, tentative, unverified, unproven, speculative, untested, on trial, under examination, on probation, under probation, on one's trial, on approval, check it out, give it a try, see how it goes, Run it up the flagpole and see who salutes.

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