necessary, requisite, compulsory, necessary, indispensable, incumbent, important

binding, essential

unavoidable, compulsory, incumbent

essentially

become necessary, be incumbent (on)

to be or become necessary (for), to follow of necessity, to be incumbent (on), to behove

make (something) incumbent or obligatory (on)

consider necessary or right, deem indispensable

closely related to each other, reciprocated (or intimate) friendship, reciprocal, reciprocated, correlative, inseparable

closely related to each other, reciprocated (or intimate) friendship, reciprocal, reciprocated, correlative, inseparable

intransitive verb

a good turn repaid by evil

justifiable homicide

Library: difference or objectionable sentence, or sign of missing letter or word

compulsory, indispensable part

intransitive infinitive

right and proper