taru-adjective, adverb taking the 'to' particle
Literary or formal word describing a proud, triumphant, or elated manner. Often used in the adverbial form 昂然と.
Convinced of victory, he puffed out his chest in triumph.
昂然たる態度で演壇に立った。
He stood at the podium with a proud demeanor.
誇らしい is a common i-adjective meaning 'proud' in a positive sense, whereas 昂然 is a stiffer, more formal term often used in written language.
Standard kanji form for this literary adjective/adverb.
Alternate kanji form; less common than 昂然.
Composed of 昂 (high-spirited, elated) and 然 (a suffix forming adjectives/adverbs describing a state). The exact historical derivation is uncertain, but the combination conveys a state of being proudly elevated.