Lewis & Short

Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.

ad-densĕo, ēre, and ăd-denso, āre (cf. Wagner ad Verg. G. 1, 248), 2 and 1, v. a., to make close, compact (very rare): extremi addensent acies, Verg. A. 10, 432 Rib.
In pass., of water, to become thick, to thicken: aquam radice ea addita addensari, Plin. 20, 21, 84, § 230.