1725, from French tumescence, from Latin tumescentem (nominative tumescens) "swelling," present participle of tumescere "begin to swell," from tumere "to swell" + inchoative suffix -escere. The earliest attested form of the word in English is tumefaction (1590s). Reference: http://www.etymonline.com/index.php?allowed_in_frame=0&search=Tumescence&searchmode=none
tumescence (plural tumescences)
- A swelling due to the presence of fluid.
- A swollen bodily organ; used especially of erectile tissue.