Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
hărēnātus (aren-), a, um, adj. [id], sanded, covered or mixed with sand (very rare): calx, Cato, R. R. 18, 7; Inscr. Grut. 207.
As subst.: hărēnātum, i (sc. opus), n., sand-mortar, Vitr. 7, 4; Plin. 36, 23, 55, § 176 sq.