astringent (a substance which draws tissue together)

to use / to employ / to make use of, to apply / to spend

(medicine) astringency / (physics) concentration of light / (biology) convergence of evolution

(medicine) to astringe; to make astringent / (physics) to concentrate light; (physics, of light) to concentrate / (biology, of evolution) to converge; to be convergent

(anatomy) skin / exterior surface

agent, chemical substance / drug, medicine / dose

drug, substance

use one thing for many purposes / work someone hard

to use one's head

(evolutionary theory) convergent evolution