Repiner is a relatively uncommon word that means "one who complains constantly" or "one who is never satisfied". If you are looking for alternative words to use instead of repiner, here are some synonyms that could be useful: grumbler, faultfinder, carper, malcontent, complainer, bellyacher, nitpicker, whiner, grouser, mope, sniveller. All of these words convey the idea of a person who is negative and always finding fault with things. Using synonyms like these can help add variety to your writing and make it more interesting to read.