taru-adjective, adverb taking the 'to' particle
Obsolete literary term describing a state of being hurried, restless, or unable to settle down. Used as a taru-adjective or adverb with と, e.g., 遑々として. Not used in modern everyday Japanese.
彼は遑々として落ち着かない様子だった。
He seemed restless and unable to settle down.
遑々たる日々を送る。
To spend one's days in a hurried, restless manner.
Common expression for 'restless, unable to settle down'. 遑々 conveys a similar meaning but is obsolete.
The exact derivation is uncertain. The kanji 遑 means 'leisure' or 'spare time', and the reduplicated form 遑々 likely developed the sense of being hurried or restless through classical usage.