The Latin source of the word “candidate”, candidatus, originally meant “clothed in white.”
But the whiteness indicated by this word differed from ordinary white, for which the Romans used albus, because it meant a glistening or shining whiteness, the whiteness of newly fallen snow in brilliant sunshine; hence, spotless purity, stainlessness.
Now it was the custom in ancient Rome, from three or four centuries before the days of Caesar until a similar period after his death, that a man who aspired to one of the high offices, consul, edile, pretor, tribune, should declare his intent to seek that office and should make public appearance clad in a pure white toga, one in which the natural whiteness of the cloth was intensified by applications of chalk rubbed into its fabric.
By implication, that man publicly declared that his character was as pure as the stainless snow; that, through this array, the voters might be assured that he sought public office with none but the highest of motives, and that he was the soul of honor and integrity.
From the color of the robe traditionally worn upon such occasions, the name candidatus became transferred to the person seeking office. Our English derivative, candidate, no longer carries the implication of stainless purity that its source conveyed, although office seekers and their adherents often try to give us such an impression.
The English word is comparatively recent; it is not recorded until a dozen years or so after the death of Shakespeare in 1616; he knew neither this word nor the related words, candor and candid, in which honesty, frankness, and fairness are still implicit.