candor is unreserved, honest, or sincere expression — the quality of saying what one actually thinks, particularly when saying less would be easier.
The word carries an implication that plain honesty is being offered at some cost to the speaker. To speak with candor is not merely to avoid lying but to volunteer what a more guarded person would withhold. That is why it attaches so naturally to feedback, disclosure, and testimony, and why a phrase like "with all due candor" works as a warning that something unwelcome is about to be said.
Its history runs through brightness. The Latin candor meant whiteness or radiance, from candēre, "to shine" — the same root behind candid, candle, and incandescent. English borrowed the literal sense first, moved to a figurative sense of purity or fairness of mind, and only later settled on frankness of speech. The metaphor survives wherever honesty is described as shedding light.
Candor is not 📝authenticity, which concerns being true to one's own character rather than truthful to another person, and it is not bluntness, which describes delivery rather than disclosure. A remark can be blunt without being candid, and candid without being unkind.