Laughter in its full range — from joy and play to mockery and derision. Sarah laughed (sachaq) at God's promise of a son; Isaac's name derives from this root. God laughs at the wicked (Ps 37:13).
The ambiguity of laughter runs through Scripture. Sarah's laugh of disbelief becomes the joy of fulfillment — her son Isaac embodies the transformation. God's derisive laugh at nations expresses sovereign confidence.
Isaac's name — Yitschaq — means 'he laughs.' The laughter that begins in Sarah's disbelief (Gen 18:12) becomes the laughter of fulfilled promise (Gen 21:6) — a model of faith vindicated.