Green’s Dictionary of Slang

(US, Southern) a social climber.

1887		T.M. Page In Ole Virginia 147: ‘He’s a half-strainer,’ said the woman, with sudden anger.
1892		Columbia Herald (TN) 6 May 1/2: We were just as good as any all-fired half-strainers who wus er setting themselfs up to be the salt of the arth.
1896		DN I 418: Half way strainer: one who tries to live above one’s true station. Southern (thought to be from N. C.).
1909		Atlantic Monthly July 136/2: I shall avail myself of the words furnished us by our Negroes, who are so wisely discerning in social matters [...] The ‘half-strainer’ [...] is born to prove that a little breeding is a dangerous thing. It is the half-strainer everywhere who does the most violence to the mother tongue.
1914		Sun (NY) 29 Mar. 5/2: De critter’s a downright half-strainer.
1929		(con. WWI) H. Odum Wings on My Feet 281: Some quality white folks on board, some po’ white trash. [...] Some half-strainers, too.
1946		(ref. to 1890s) PADS VI 16: Half-strainer [...] A social climber.