Needed; essential: missing several required parts. (adjective)
Obligatory: required reading. (adjective)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "required" in a sentence
"The cross-referenced section 5000A(e)(1)(B) defines the term "required contribution" for this purpose as "the portion of the annual premium which would be paid by the individual… for self-only coverage.""
"'Lactation' was the title required a heightened level of perception to come to terms with."
"But their later mode of development, the degree of perfection acquired by the egg and germ before being laid, the term required for the germ to come to maturity, as well as the frequency and regularity of the broods, are all features varying with the different kinds of animals."