The word "glibness" comes from the word "glib", which is likely a modification of the Low German word glibberig, meaning "slippery".   During the Hanseatic period (from about 1300 to about 1600), Middle Low German was the leading written language in the north of Central Europe and served as a lingua franca in the northern half of Europe.  The earliest known use of "glib" as an adjective is from 1584, in the writing of H. Plat.  The earliest known use of "glibness" in English was in 1611, by the lexicographer Randle Cotgrave. 

"Glib" is used to describe someone who is confident but too simple and lacks careful thought. For example, you might describe a car salesman who uses a polished sales pitch to sell lemons as glib. When used to describe someone's speech, "glib" implies that something is simple or easy, or that there are no problems involved, when this is not the case. 

Just the facts:

Glib Definition & Meaning - Merriam-Webster

GLIBNESS Synonyms: 50 Similar and Opposite Words | Merriam-Webster Thesaurus

GLIBNESS Definition & Meaning | Dictionary.com

I am starting to really worry about M-W, I had to out source for today's definition.