mercilessly; ruthlessly
Adverbial form of 情け容赦ない, meaning without mercy or pity; used in formal or emphatic contexts.
He attacked the enemy mercilessly.
The boss pointed out the mistakes ruthlessly.
容赦なく is a more common and slightly less intense adverb meaning 'without mercy' or 'relentlessly'. 情け容赦なく adds 情け (sympathy) for extra emphasis on pitilessness.
Standard kanji spelling.
Variant using 無 for なく; less common but still seen.
Compound of 情け (sympathy, mercy) + 容赦 (pardon, forgiveness) + なく (adverbial form of ない). The combination reinforces the sense of complete mercilessness.