taru-adjective, adverb taking the 'to' particle
assiduously; with unremitting zeal
Rare literary four-character compound describing diligent, tireless effort. Often used in formal or written contexts.
He devoted himself assiduously to his research.
Standard kanji form using 々 iteration marks. Rare and literary.
Full kanji form without iteration marks. Even rarer.
A yojijukugo (four-character compound) combining 孜々 (diligent) and 営々 (tireless effort). The exact historical derivation is uncertain; the spelling is conventionally associated with these meanings.