resulting from or showing a lack of sense; ill-considered; unwise

a foolish action, a foolish speech.

lacking forethought or caution.

trifling, insignificant, or paltry.

noun

care , carefulness , caution , circumspection , prudence , sense , seriousness , thoughtfulness , wiseness

noun

absurdity , absurdness , bunk * , carrying-on , claptrap * , craziness , dumb trick , folly , foolery , fool trick , horse feathers , impracticality , imprudence , inanity , indiscretion , insanity , insensibility , irrationality , irresponsibility , ludicrousness , lunacy , mistake , poppycock * , preposterousness , rubbish * , senselessness , silliness , stupidity , tommyrot , twaddle , unreasonableness , unwiseness , weakness , witlessness , idiocy , imbecility , madness , nonsense , tomfoolery , zaniness , balderdash , bunk , drollery , fatuity , horseplay , ineptitude , insagacity , puerility , unwisdom