These two words overlap somewhat, but usually the word you want is “hearty.” The standard expressions are “a hearty appetite,” “a hearty meal,” a “hearty handshake,” “a hearty welcome,” and “hearty applause.” “Hardy” turns up in “hale and hardy,” but should not be substituted for “hearty” in the other expressions. “Party hearty” and “party hardy” are both common renderings of a common youth saying, but the first makes more sense.
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