Antonyms of adj pensive

2 senses of pensive

Sense 1
brooding, broody, contemplative, meditative, musing, pensive, pondering, reflective, ruminative -- (deeply or seriously thoughtful; "Byron lives on not only in his poetry, but also in his creation of the 'Byronic hero' - the persona of a brooding melancholy young man";)

INDIRECT (VIA thoughtful) -> thoughtless -- (showing lack of careful thought; "the debate turned into thoughtless bickering")

Sense 2
pensive, wistful -- (showing pensive sadness; "the sensitive and wistful response of a poet to the gentler phases of beauty")

INDIRECT (VIA sad) -> glad -- (showing or causing joy and pleasure; especially made happy; "glad you are here"; "glad that they succeeded"; "gave a glad shout"; "a glad smile"; "heard the glad news"; "a glad occasion")

Similarity of adj pensive

2 senses of pensive

Sense 1
brooding, broody, contemplative, meditative, musing, pensive, pondering, reflective, ruminative -- (deeply or seriously thoughtful; "Byron lives on not only in his poetry, but also in his creation of the 'Byronic hero' - the persona of a brooding melancholy young man";)
       => thoughtful (vs. thoughtless) -- (exhibiting or characterized by careful thought; "a thoughtful paper")

Sense 2
pensive, wistful -- (showing pensive sadness; "the sensitive and wistful response of a poet to the gentler phases of beauty")
       => sad (vs. glad) -- (experiencing or showing sorrow or unhappiness; "feeling sad because his dog had died"; "Better by far that you should forget and smile / Than that you should remember and be sad"- Christina Rossetti)