Antonyms of adj needless

1 sense of needless

Sense 1
gratuitous, needless, uncalled-for -- (unnecessary and unwarranted; "a strikers' tent camp...was burned with needless loss of life")

INDIRECT (VIA unnecessary) -> necessary -- (absolutely essential)

Similarity of adj needless

1 sense of needless

Sense 1
gratuitous, needless, uncalled-for -- (unnecessary and unwarranted; "a strikers' tent camp...was burned with needless loss of life")
       => unnecessary (vs. necessary), unneeded -- (not necessary)