suffixed to words indicating a class of people to create a plural (esp. in impolite contexts)

cause, origin, source

principle, general rule, as a rule...

plaintiff, accuser, prosecutor

starting point, origin, beginning...

atomic bomb, A-bomb

crude oil

principle, theory, fundamental truth

atomic energy, nuclear power

manuscript, copy, draft...

original work

raw materials, ingredient

atom

tableland, plateau

grassy field, grassland, meadow...

dry riverbed, river beach

dry riverbed, river beach

origin, beginning, source...

nuclear power plant, nuclear power generation, primary (e.g. primary immunodeficiency syndrome)

origin, beginning, genesis...

element, chemical element, (classical) element (e.g. earth...

open field, empty lot, plain

original plan, original bill, original motion...

original document (not a copy or adaptation), book in its original language (esp. a European language)

origin of a word, derivation of a word, etymology

field, plain, prairie...

Japanese writing paper (lined with a square grid, one square per character), manuscript paper

middle of a field, middle of a country, field of contest

atomic reactor, nuclear reactor

motive power, driving force