observative
/əbˈzəːvətɪv/ /ɒbˈzəːvətɪv/Now rare
adjective
Of, relating to, consisting of, or based on observation; given to observation, observant, attentive, heedful.
Origin
Early 17th century (in an earlier sense). From classical Latin observāt-, past participial stem of observāre observe + -ive.