The explanation of Isaac's name (from a word meaning «laughter») is indicated in the thrice - repeated
narrative motif of laughter
over the idea and fact of Isaac's birth (17:17, 18:12, 21:6) So is Ishmael's (16:11, 17:20, 21:17) The meaning «heelholder» is given to the name Jacob with the explanation that he was born holding his twin brother by the heel (25:26).