taru-adjective, adverb taking the 'to' particle
pent-up; burning; irrepressible
Formal literary term describing strong emotions, energy, or ambition that are held back and ready to burst forth. Often used with たる or として.
彼の胸には鬱勃たる野心が秘められていた。
A burning ambition was hidden in his heart.
He could not suppress the irrepressible creative urge welling up inside him.
Compound of 鬱 (dense, gloomy, pent-up) and 勃 (sudden, vigorous). The combination suggests suppressed energy that is about to burst forth. The exact historical derivation is uncertain.