sink·hole 
(sĭngkhōl′)
(sĭngkhōl′)n.
A natural depression formed by the undermining or sudden collapse of the land surface, often as a result of groundwater enlarging cavities in underlying limestone or other easily soluble bedrock.
- straight-laced
- straight-laced
- straight-line
- straightly
- straight man
- straightness
- straight off
- straight-out
- straight poker
- straight razor
- straight shooter
- straight-shooting
- straight ticket
- straight up
- straightway
- strain
- strain
- strain at stool
- strained
- strainer
- strain every nerve
- strain gauge
- straining beam
- strainometer
- strait