Whatever; used to indicate that the speaker would do the same thing regardless of the options.(pronoun)
Definitely, under all and any circumstances.(adverb)
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Use "no matter what" in a sentence
"Cavorting with a potential witness, victim, or suspect was bad business, no matter what the cost of survival."
"Students who earn First Honors are always given their choice of courses, no matter what those of us who know better might think, she said, the jowls flapping around."
"Most of its essential features can well be reatined and will prove advantageous no matter what new branches of study or methods of teaching are introduced."