onion butter(n = noun.food) - butter blended with minced onion;
is a kind of paste, spread

anchovy butter, apple butter, bercy butter, bermuda onion, bread and butter, bread and butter pickle, brown butter, brown onion sauce, butter, butter and eggs, butter bean, butter churn, butter cookie, butter daisy, butter dish, butter knife, butter up, clarified butter, climbing onion, cocoa butter, colbert butter, drawn butter, egyptian onion, flowering onion, garlic butter, green onion, hooker's onion, lemon butter, lobster butter, meuniere butter, multiplier onion, nodding onion, nodding wild onion, nut butter, onion, onion bagel, onion bread, onion dome, onion louse, onion mildew, onion plant, onion roll, onion salt, onion smut, onion stem, onion thrips, onion yellow dwarf, onion yellow-dwarf virus, peanut butter, pimento butter, purple onion, red onion, red-skinned onion, sea onion, shrimp butter, snail butter, spanish onion, spring onion, top onion, tree onion, vidalia onion, welsh onion, white onion sauce, wild onion, witches' butter, yak butter