taru-adjective, adverb taking the 'to' particle
aimless; rambling; desultory; casual
Describes doing something without a clear purpose, plan, or focus, often with a sense of drifting or being haphazard. Used as a たる adjective or adverbially with と.
彼は漫然と街を歩いていた。
He was wandering aimlessly through the streets.
漫然たる日々を過ごすのはもったいない。
It's a waste to spend your days in a desultory manner.