Enervate is a tricky word. At first glance, you might think enervate . . . energize . . . invigorate — and you'd be wrong. Enervate means to deprive of strength, force, or vigor; to weaken physically, mentally, or morally; to devitalize or debilitate. Its synonyms are unnerve and weaken.
An easy way to remember the meaning is to look at its Latin roots: e-, out + nervus, nerve.
In Tess of the d'Urbervilles, author Thomas Hardy describes Talbothays Dairy at the height of summer:
The air of the place, so fresh in the spring and early summer, was stagnant and enervating now. Its heavy scents weighed upon them, and at mid-day the landscape seemed lying in a swoon. Ethiopic scorchings browned the upper slopes of the pastures, but there was still bright green herbage here where the watercourses purled.