adjective
An adjective is a word that describes or gives more information about a noun or pronoun. In this case, 'untiring' describes someone or something that does not tire or become exhausted easily.
Her untiring efforts in the research project were truly commendable.
She's been untiring in her pursuit of that promotion.
He's like an untiring energizer bunny when it comes to partying.
The untiring flow of the river symbolized the unstoppable force of nature.