candidyoudaoicibaDictYouDict[candid 词源字典]
candid: [17] Originally, candid meant simply ‘white’; its current sense ‘frank’ developed metaphorically via ‘pure’ and ‘unbiased’. English acquired the word, probably through French candide, from Latin candidum, a derivative of the verb candēre ‘be white, glow’ (which is related to English candle, incandescent, and incense).

The derived noun candour is 18th-century in English. Candida, the fungus which causes the disease thrush, got its name from being ‘white’. And in ancient Rome, people who were standing for election wore white togas; they were thus called candidāti, whence English candidate [17].
=> candidate, candle, incandescent, incense[candid etymology, candid origin, 英语词源]
candid (adj.)youdaoicibaDictYouDict
1620s, "white," from Latin candidum "white; pure; sincere, honest, upright," from candere "to shine," from PIE root *kand- "to glow, to shine" (see candle). In English, metaphoric extension to "frank" first recorded 1670s (compare French candide "open, frank, ingenuous, sincere"). Of photography, 1929. Related: Candidly; candidness.