ETYMOLOGY
from think (vb.) + -ative, chiefly after talkative
EXAMPLE
“… They have not known I say, that the knowledge of Observation, doth not introduce an understanding into the essential thingliness of a thing, but erecteth only a thinkative knowledge: For otherwise, the understanding should perceive causes that are before in essence. Then also they have been deceived by the simplicity of the Water, which simpleness they have confounded with the unity of knowledge to us unknown. …”
From: Oriatrike or, Physick Refined
By Jean Baptiste van Helmont
Translated by J. Chandler, 1662
Lexicophilia 