unrelenting
Concise Oxford English Dictionary © 2008 Oxford University Press:
unrelenting/ʌnrɪˈlentɪŋ/
▶adjective not yielding in strength, severity, or determination.
– derivatives
unrelentingly adverb,
unrelentingness noun.
unrelentingly adverb,
unrelentingness noun.
'unrelenting' also found in these Oxford entries:

