late 14c., sentement, "personal experience, one's own feeling," from Old French santement, sentement (12c.) and directly from Medieval Latin sentimentum "feeling, affection, opinion," from Latin sentire "to feel" (see sense (n.)).
The original sense was obsolete after Middle English. From early 15c. as "intention, inclination." The meaning "what one feels about something, thought, opinion, notion" (1630s) and modern spelling seem to be a re-introduction from French (where it was spelled sentiment by 17c.).
In this sense a vogue word by mid-18c. with wide application, commonly "higher feeling, a thought colored by or proceeding from emotion," especially as expressed in literature or art (by 1709). The 17c. sense is preserved in phrases such as my sentiments exactly.