I. noun
( -s )
Etymology: Middle English fastinge, fasting, from fasten to fast + -inge, -ing -ing — more at fast V
: the act of abstaining from food especially for an unusual time and often as a form of religious observance or for therapeutic purposes
II. adjective
Etymology: from present participle of fast (V)
: of or from a fasting subject
fasting urine
fasting blood-sugar level