A liquid, such as turpentine, mixed with paint or varnish to reduce its viscosity and make it easier to apply.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "thinner" in a sentence
"Much of the coal thats left is of poorer quality or its in thinner, more deeply buried seams."
"The film should probably be seen by all health professionals dealing with obesity - especially those, who widely promote the general ideology that thinner is healthier (even though epidemiological studies clearly tell us that this IS NOT THE CASE!)."
"Children who have had a mechanical valve surgically placed will need routine monitoring to make sure that the blood thinner is creating just the right amount of thinning effect."