without reserve; frankly; openly
Used when speaking one's mind honestly and without holding back. Often appears in formal or written contexts.
Please state your opinion frankly.
He spoke his thoughts without reserve.
From 腹蔵 (ふくぞう, 'keeping in one's heart') + なく ('without'). The exact historical derivation is uncertain, but the expression is conventionally associated with the idea of not hiding one's true thoughts.