/ ɪmˈplækəbl; NAmE / adjective
1.
( of strong negative opinions or feelings ) that cannot be changed :
implacable hatred
2.
( of a person ) unwilling to stop opposing sb/sth :
an implacable enemy
► im·plac·ably / ɪmˈplækəbli; NAmE / adverb :
to be implacably opposed to the plan
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WORD ORIGIN
late Middle English : from Latin implacabilis , from in- not + placabilis (from placare appease).