This word’s obsolete meaning of desire descends from earlier meanings such as pleasure and delight, spotted in King Alfred’s translation of Boethius around the year 888.  The parallel and interlocked meaning of sexual desire is attested from about the year 1000, and seems to be locked with the descriptor “fleshly” in theological writings for a few centuries.

• 12.015 but the splendour, the lust,
• 15.049 and the lust of it was heavy on him.

“lust, n.” OED Online. Oxford University Press, March 2015. Web. 20 May 2015.