in half—
1. divide or tear into two equal parts:
- He and Meyer each signed half of a one dollar bill, tore it in half and kept each other’s halves, just for good luck.
2. (also: by half ) reduce by fifty percent of the original amount:
- He had priced rolltops in a downtown department store and knew he had cut the cost in half.
in halves — = in half 1:
- When a square cut in halves makes two triangles, those two triangles are still only the two halves of the square.