A relative close enough to be kissed in salutation, hence anyone with whom a person is fairly intimate: The two species will often prove to be kissing cousins, for they'll crossbreed/ You guys talk like kissing cousins
A close copy: He had a kissing cousin of Montgomery's mustache(1940s+)
The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with kissing cousins
Two or more things that are closely akin or very similar. For example, They may be made by different manufacturers, but these two cars are kissing cousins. This metaphoric term alludes to a distant relative who is well known enough to be greeted with a kiss.
[ c. 1930