-plus Look up -plus at Dictionary.com
word-forming element, Latin -plus "-fold." Watkins derives it from *-plo-, combining form of PIE *pel- (3) "to fold" (see fold (v.)) and makes it cognate with Old English -feald, Greek -paltos, -plos. But De Vaan connects it to the root that means "much, many, more" and is the source of poly-.