明かす
あかす · akasu · JLPT N1 · verb-godan
to reveal
🌙☕ 明 (bright) + かす: to make bright, to bring out into the light. Stay up all night and the dawn reveals the truth.
明かす = 明 (light, dawn) + かす (causative: make). Revealing a secret brings it into the light; staying up until 明 (dawn) is 'making the night bright' - so both meanings share the light root.