When a hooker\prostitute relinquishes their services without charge. Most often in the form of a blow job.
The hooker in Vegas felt so bad for Jim that she went back to his room with him pro blowno. That almost NEVER happens!
Problowno reffers to a free blowjob without strings. Like free legal representation but a blowjob.
We met at a bar and she went pro-blowno.