libido (n.) Look up libido at Dictionary.com
"psychic drive or energy, usually associated with sexual instinct," 1892, carried over untranslated in English edition of Krafft-Ebing's "Psychopathia Sexualis"; and used in 1909 in A.A. Brill's translation of Freud's "Selected Papers on Hysteria" (Freud's use of the term led to its popularity); from Latin libido "desire, lust," from libere "to be pleasing, to please," ultimately cognate with Old English lufu (see love (n.)).