taru-adjective, adverb taking the 'to' particle
strong moral fiber; backbone; unyielding spirit
A yojijukugo describing a person of firm principles and unshakable determination. Often used in literary or formal contexts.
彼は気骨稜々たる政治家だ。
He is a politician of strong moral fiber.
気骨稜々として、どんな困難にも屈しなかった。
With unyielding spirit, he never gave in to any hardship.
気骨 alone means 'backbone' or 'moral strength', but 気骨稜々 is a more emphatic, literary four-character compound.
A yojijukugo combining 気骨 (backbone, moral strength) and 稜々 (towering, imposing). The exact origin is uncertain, but it follows a common pattern of intensifying a quality with a reduplicative or emphatic second element.