1. [1910s+] a conventional, respectable person, as opposed to a criminal.
2. [1930s+] conventional heterosexual intercourse in the face to-face ‘missionary position’; thus in prostitute’s use, straight date n., one who desires conventional intercourse; straight girl n., a prostitute who only offers such a service; also pornography featuring this.
3. [1960s+] (orig. gay) a heterosexual person.
4. [1960s+] (also straight-head) used by members of the ‘counter-culture’ to describe a member of Establishment society.
5. [1990s+] (US campus) one who stands outside the current social norms.
[1970s] (US gay) a heterosexual male.
[late 19C] to abandon a respectable life for criminality.