The Collaborative International Dictionary of English v.0.48:
Thin \Thin\, v. t. [imp. & p. p. Thinned; p. pr. & vb. n. Thinning.] [Cf. AS. ge[thorn]ynnian.] To make thin (in any of the senses of the adjective). [1913 Webster]WordNet (r) 3.0 (2006):
thinned adj 1: mixed with water; "sold cut whiskey"; "a cup of thinned soup" [syn: cut, thinned, weakened]