1590s, "smooth and slippery," a dialect word, possibly a shortening of obsolete glibbery "slippery," which is perhaps from Low German glibberig "smooth, slippery," from Middle Low German glibberich, from or related to glibber "jelly," all part of the Germanic group of gl- words for "smooth, shining, joyful," from PIE root *ghel- (2) "to shine." Of words, speakers, etc., from c. 1600. Related: Glibly; glibness.