The Hebrew word ZNH (zonah/zanah) is translated into Greek as 'porneia', and Christians translate it as 'prostitution'.

As Irene Reigner concludes, the meaning is to “participate in non-Yahwist religious praxis.” i.e. to worship other gods.

I wrote a post on 'porneia' here. It's used in non-sexual settings of improper worship etc.

https://medium.com/belover/christianitys-porneia-problem-5df11c1e1db

There is no rule against unmarried sex!