From WordNet (r) 3.0 (2006) [wn]:
whitewater
n 1: frothy water as in rapids or waterfalls [syn: {white
water}, whitewater]
From The Collaborative International Dictionary of English v.0.48 [gcide]:
Rapid \Rap"id\, Rapids \Rap"ids\(r[a^]p"[i^]dz), n. [Cf. F.
rapide. See Rapid, a.]
The part of a river where the current moves with great
swiftness, but without actual waterfall or cascade; sometimes
called whitewater; -- usually used in the plural; as, the
Lachine rapids in the St. Lawrence. For boaters on the river,
it is a place that can be hazardous, with danger of capsizing
or crashing into large rocks.
[1913 Webster +PJC]
Row, brothers, row, the stream runs fast,
The rapids are near, and the daylight's past. --Moore.
[1913 Webster] Rapid-fire
From The Collaborative International Dictionary of English v.0.48 [gcide]:
White-water \White"-wa`ter\, n. (Far.)
A dangerous disease of sheep.
[1913 Webster]