Control arm

Double Wishbone Suspension

In automotive suspension, a control arm (sometimes called a wishbone or A-arm) is a nearly flat and roughly triangular member (or sub-frame), that pivots in two places. The broad end of the triangle attaches at the frame and pivots on a bushing. The narrow end attaches to the steering knuckle and pivots on a ball joint.

Two such devices per wheel make up double wishbone suspension, while one control arm per wheel makes up a part, usually the lower part, of MacPherson strut suspension or of various other configurations.

References

Car suspension at Howstuffworks.com