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The Collaborative International Dictionary
Subtiliate

Subtiliate \Sub*til"i*ate\, v. t. [LL. subtiliare.] To make thin or rare. [Obs.]
--Harvey. -- Sub`til*i*a"tion, n. [Obs.]
--Boyle.

Wiktionary
subtiliate

vb. (context obsolete transitive English) To make thin or rare; to rarefy.