Faute de mieux is French and is defined as for lack of something better.(adverb)
An example of faute de mieux used as an adverb is in the following sentence: "He headed west faute de mieux," which means he headed west to find something better.
See faute de mieux in Webster's New World College Dictionary
See faute de mieux in American Heritage Dictionary 4
Origin: : faute, lack
Origin: + de, of
Origin: + mieux, better.