rapids is a form of:

Rapid



noun
1.
ជួរ (កន្លែងទឹកហូរខ្លាំងតាមទន្លេ ព្រែក)
adjective
1.
(quick, swift, fast. -rapids place in a river or stream where the water flows especially fast because of a steep slope in the river ved) rapid growth យ៉ាងឆាប់រហ័ស, rapid worker ដែលលឿន
2.
(បច្ចេកទេស) លឿន, រហ័ស
ENGLISH MEANING
noun
1.
The part of a river where the current moves with great swiftness, but without actual waterfall or cascade; -- usually in the plural; as, the Lachine rapids in the St. Lawrence.
adjective
1.
Very swift or quick; moving with celerity; fast; as, a rapid stream; a rapid flight; a rapid motion.
2.
Advancing with haste or speed; speedy in progression; in quick sequence; as, rapid growth; rapid improvement; rapid recurrence; rapid succession.
3.
Quick in execution; as, a rapid penman.