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tantear (Verb) "to estimate"
Late 15th cent. Probably verb formed from tanto, though the semantics are hazy.
Corominas, J. & J. Pascual. Diccionario crítico etimológico castellano e híspanico. 6 vols. Madrid: Gredos. 1991-1997.
Real Academia Española. Diccionario de la lengua española. Online. 23rd ed. Madrid: Espasa Calpa. 2014. http://www.rae.es/.