early 14c., "discomfort, inconvenience, distress, trouble," from Old French desaise "lack, want; discomfort, distress; trouble, misfortune; disease, sickness," from des- "without, away" (see dis-) + aise "ease" (see ease (n.)). Restricted pathological sense of "sickness, illness" in English emerged by late 14c.; the word still sometimes was used in its literal sense early 17c., and was somewhat revived 20c., usually with a hyphen (dis-ease).
mid-14c., disesen, "to make uneasy; inflict pain," a sense now obsolete; late 14c. as "to have an illness or infection;" late 15c. as transitive, "to infect with a disease, make ill;" from disease (n.).