Antonyms of adj day-by-day

1 sense of day-by-day

Sense 1
daily, day-to-day, day-by-day, day-after-day -- (of or belonging to or occurring every day; "daily routine"; "a daily paper")

INDIRECT (VIA periodic) -> aperiodic, nonperiodic -- (not recurring at regular intervals)

Similarity of adj day-by-day

1 sense of day-by-day

Sense 1
daily, day-to-day, day-by-day, day-after-day -- (of or belonging to or occurring every day; "daily routine"; "a daily paper")
       => periodic (vs. aperiodic), periodical -- (happening or recurring at regular intervals; "the periodic appearance of the seventeen-year locust")

Synonyms of adv day-by-day

1 sense of day by day

Sense 1
day by day, daily -- (gradually and progressively; "his health weakened day by day")