IPA: /rɪˈlɛntləs/
KK: /rɪˈlɛntləs/
Continuing without stopping or becoming less intense; not giving up or letting up.
The team's relentless effort led them to victory in the championship.
Comparative: more relentless
Superlative: most relentless
Relentless is formed from "re-" (meaning back or again) and "lent" (from Latin "lentus", meaning slow or yielding) combined with the suffix "-less" (meaning without). The word describes a state of being without yielding or being slow to give up, hence, unyielding or persistent.
Think of someone who is 'without' ('-less') any 'yielding' ('lent') — that's why relentless means not giving up.