Antonyms of adj robust

4 senses of robust

Sense 1
robust (vs. frail) -- (sturdy and strong in form, constitution, or construction; "a robust body"; "a robust perennial")

frail (vs. robust) -- (physically weak; "an invalid's frail body")
        => decrepit, debile, feeble, infirm, rickety, sapless, weak, weakly -- (lacking bodily or muscular strength or vitality; "a feeble old woman"; "her body looked sapless")
        => light-boned -- (having a bone structure that is light with respect to the surrounding flesh)

Sense 2
full-bodied, racy, rich, robust -- (marked by richness and fullness of flavor; "a rich ruby port"; "full-bodied wines"; "a robust claret"; "the robust flavor of fresh-brewed coffee")

INDIRECT (VIA tasty) -> tasteless -- (lacking flavor)

Sense 3
robust -- (strong enough to withstand or overcome intellectual challenges or adversity; "the experiment yielded robust results"; "a robust faith")

INDIRECT (VIA strong) -> weak -- (wanting in physical strength; "a weak pillar")

Sense 4
robust -- (rough and crude; "a robust tale")

INDIRECT (VIA unrefined) -> refined -- ((used of persons and their behavior) cultivated and genteel; "she was delicate and refined and unused to hardship"; "refined people with refined taste")

Similarity of adj robust

4 senses of robust

Sense 1
robust (vs. frail) -- (sturdy and strong in form, constitution, or construction; "a robust body"; "a robust perennial")
       => beefy, burly, husky, strapping, buirdly -- (muscular and heavily built; "a beefy wrestler"; "had a tall burly frame"; "clothing sizes for husky boys"; "a strapping boy of eighteen"; "`buirdly' is a Scottish term")
       => big-boned -- (having a bone structure that is massive in contrast with the surrounding flesh)
       => big-chested, chesty -- (marked by a large or well-developed chest; "he was big-chested, big-shouldered and heavy-armed")
       => big-shouldered, broad-shouldered, square-shouldered -- (having broad shoulders; "big-shouldered and heavy-armed")
       => cast-iron, iron -- (extremely robust; "an iron constitution")
       => hardy, stalwart, stout, sturdy -- (having rugged physical strength; inured to fatigue or hardships; "hardy explorers of northern Canada"; "proud of her tall stalwart son"; "stout seamen"; "sturdy young athletes")
       => hardy -- (able to survive under unfavorable weather conditions; "strawberries are hardy and easy to grow"; "camels are tough and hardy creatures")
       => half-hardy -- ((of plants) requiring protection from frost; "half-hardy annuals")
       => heavy-armed -- (having massive arms; "he was big-chested, big-shouldered and heavy-armed")
       => square-built -- (broad and solidly built)
       => vigorous -- (strong and active physically or mentally; "a vigorous old man who spent half of his day on horseback"- W.H.Hudson)
          Also See-> healthy#1; rugged#1; strong#1

Sense 2
full-bodied, racy, rich, robust -- (marked by richness and fullness of flavor; "a rich ruby port"; "full-bodied wines"; "a robust claret"; "the robust flavor of fresh-brewed coffee")
       => tasty (vs. tasteless) -- (pleasing to the sense of taste; "a tasty morsel")

Sense 3
robust -- (strong enough to withstand or overcome intellectual challenges or adversity; "the experiment yielded robust results"; "a robust faith")
       => strong (vs. weak) -- (having strength or power greater than average or expected; "a strong radio signal"; "strong medicine"; "a strong man")

Sense 4
robust -- (rough and crude; "a robust tale")
       => unrefined (vs. refined) -- ((used of persons and their behavior) not refined; uncouth; "how can a refined girl be drawn to such an unrefined man?")