Antonyms of adj gullible

2 senses of gullible

Sense 1
fleeceable, green, gullible -- (naive and easily deceived or tricked; "at that early age she had been gullible and in love")

INDIRECT (VIA naive) -> sophisticated -- (having or appealing to those having worldly knowledge and refinement and savoir-faire; "sophisticated young socialites"; "a sophisticated audience"; "a sophisticated lifestyle"; "a sophisticated book")

Sense 2
gullible -- (easily tricked because of being too trusting; "gullible tourists taken in by the shell game")

INDIRECT (VIA unwary) -> wary -- (marked by keen caution and watchful prudence; "they were wary in their movements"; "a wary glance at the black clouds"; "taught to be wary of strangers")

Similarity of adj gullible

2 senses of gullible

Sense 1
fleeceable, green, gullible -- (naive and easily deceived or tricked; "at that early age she had been gullible and in love")
       => naive (vs. sophisticated), naif -- (marked by or showing unaffected simplicity and lack of guile or worldly experience; "a teenager's naive ignorance of life"; "the naive assumption that things can only get better"; "this naive simple creature with wide friendly eyes so eager to believe appearances")

Sense 2
gullible -- (easily tricked because of being too trusting; "gullible tourists taken in by the shell game")
       => unwary (vs. wary) -- (not alert to danger or deception; "the shrieks of unwary animals taken by surprise"; "some thieves prey especially on unwary travelers"; "seduce the unwary reader into easy acquiescence"- O.J.Campbell)