humidify (v.)

"moist or accompanied with moisture; containing, or formed or effected by, water or vapor; wet, damp," early 15c., from Old French humide, umide "damp, wet" (15c.) or directly from Latin humidus "moist, wet," variant (probably by influence of humus "earth") of umidus, from umere "be moist, be wet," from Proto-Italic *umo- "wet" (also source of Latin umidus "wet, moist," umiditas "moisture," umor "moisture, fluid," umectus "moist, wet"), perhaps from PIE *uhrmo- "wet," from the same source as Latin urina [de Vaan].

word-forming element meaning "make, make into," from French -fier, from Latin -ficare, combining form of facere "to make" (from PIE root *dhe- "to set, put").