Is it ensure, insure, or assure?
1630s, "capable of feeling," from Latin sentientem (nominative sentiens) "feeling," present participle of sentire "to feel" (see sense (n.)). Meaning "conscious" (of something) is from 1815.
sentient sen·tient (sěn'shənt, -shē-ənt)adj.
Having sense perception; conscious.
Experiencing sensation or feeling.