Antonyms of adj sure-fire

1 sense of sure-fire

Sense 1
sure-fire -- (certain to be successful; "a sure-fire way to get rich")

INDIRECT (VIA successful) -> unsuccessful -- (not successful; having failed or having an unfavorable outcome)

Similarity of adj sure-fire

1 sense of sure-fire

Sense 1
sure-fire -- (certain to be successful; "a sure-fire way to get rich")
       => successful (vs. unsuccessful) -- (having succeeded or being marked by a favorable outcome; "a successful architect"; "a successful business venture")