"to make secure, safe, firm" (akin to asphales, "safe"), (a, negative, and sphallo, "to trip up"), is translated "make ... fast," in Acts 16:24 , of prisoners' feet in the stocks. In Matthew 27:64,65,66 , it is rendered "to make sure." See SURE.
Note: For HOLD (fast) and STAND (fast), see HOLD and STAND, No. 7.