Diluent

Dil"u*ent, n. 1. That which dilutes.

2. (Med.) An agent used for effecting dilution of the blood; a weak drink.

There is no real diluent but water.
Arbuthnot.

Dil"u*ent (?), a. [L. diluens, p. pr. diluere. See Dilute.] Diluting; making thinner or weaker by admixture, esp. of water. Arbuthnot.