field vs flood plain

field and flood plain both are nouns.

Word	Noun	Adjective	Verb	Adverb
field	Yes	No	Yes	No
flood plain	Yes	No	No	No

As nouns, flood plain is a hyponym of field; that is, flood plain is a word with a more specific, narrower meaning than field:

field: extensive tract of level open land
flood plain: a low plain adjacent to a river that is formed chiefly of river sediment and is subject to flooding

Other hyponyms of field include flat, floodplain, llano, moor, moorland, peneplain, peneplane, snowfield, steppe, tundra.

field (noun)	flood plain (noun)
a particular kind of commercial enterprise	a low plain adjacent to a river that is formed chiefly of river sediment and is subject to flooding
a place where planes take off and land
a branch of knowledge
the area that is visible (as through an optical instrument)
(mathematics) a set of elements such that addition and multiplication are commutative and associative and multiplication is distributive over addition and there are two elements 0 and 1
all of the horses in a particular horse race
all the competitors in a particular contest or sporting event
(computer science) a set of one or more adjacent characters comprising a unit of information
a piece of land cleared of trees and usually enclosed
somewhere (away from a studio or office or library or laboratory) where practical work is done or data is collected
a piece of land prepared for playing a game
a region in which active military operations are in progress
a region where a battle is being (or has been) fought
a geographic region (land or sea) under which something valuable is found
extensive tract of level open land
the space around a radiating body within which its electromagnetic oscillations can exert force on another similar body not in contact with it
a particular environment or walk of life

field (verb)	flood plain (verb)
select (a team or individual player) for a game
answer adequately or successfully
play as a fielder
catch or pick up (balls) in baseball or cricket