Definitions

1. adjective

not having the water drained from it; especially of a spring or a swamp

“The park ranger warned hikers about the undrained areas of the marsh.”

2. verb

to leave or prevent the draining of (something)

“The engineer decided to undrain the reservoir to prevent water shortages.”

3. noun

a spring or swamp that is undrained

“The scientist studied the undrained areas of the wetland.”