Antonyms of adj worthful

1 sense of worthful

Sense 1
valuable, worthful -- (having worth or merit or value; "a valuable friend"; "a good and worthful man")

INDIRECT (VIA worthy) -> unworthy -- (lacking in value or merit; "dispel a student whose conduct is deemed unworthy"; "unworthy of forgiveness")

Similarity of adj worthful

1 sense of worthful

Sense 1
valuable, worthful -- (having worth or merit or value; "a valuable friend"; "a good and worthful man")
       => worthy (vs. unworthy) -- (having worth or merit or value; being honorable or admirable; "a worthy fellow"; "a worthy cause")