Diluent

a.	1.	Diluting; making thinner or weaker by admixture, esp. of water.
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.

Noun

1.

diluent - a diluting agent Synonyms: dilutant, thinner

agent, dilutant, thinner