taru-adjective, adverb taking the 'to' particle
vast; wide; spacious; extensive
Rare literary term used in classical or highly formal writing to describe something vast and boundless, such as the sea, sky, or a grand vision. Often appears in the adverbial form 浩蕩として.
浩蕩たる大海原を前に、言葉を失った。
Before the vast expanse of the ocean, I was lost for words.
彼の構想は浩蕩として掴みどころ
His vision is so vast and boundless that it's hard to grasp.
広大 is the common word for 'vast' or 'extensive' in modern Japanese, while 浩蕩 is a rare literary synonym.
茫洋 also means 'boundless' or 'vast', often with a nuance of haziness or obscurity, and is more common than 浩蕩.
The kanji 浩 means 'wide expanse of water' or 'vast', and 蕩 means 'melt' or 'vast'. The compound is of Chinese origin (kango) and is used in classical literature to describe boundlessness.