RESPONSE GIVEN BY JOSEPH ISLAM
[Please contact Joseph Islam for further details of the original thread]
Peace brother [Name Removed]
'Fahisha' is anything which is evil, an excess, an enormity, immoderate, beyond measure or an excessive sin. So something which is gross, or lewd and obscene. This excess can also apply to speech or language (as in uttering foul, evil, lewd or obscene speech).
Note how 'fahishatu' is used as excess (in slander / scandal in speech) in 24:19
24:19 Surely, those who love to see immorality (Arabic: fahishatu) spread among the believers, shall be punished in this world and in the life to come. For, God knows and you do not know.
Now the 'fahisha' here given the context of the narrative dealing with slander is not referring to sexual immorality, but a reference to slander or obscene or transgressed speech by those amongst the believers that spread slander.
There is no 'fahisha' in 24:2. The terms used are 'zaniyatu' (female) and 'zani' (male) which means one that commits fornication / adultery (zina).
So yes, 'zina' can be considered as a form of fahisha but not all 'fahisha' is 'zina'.
Therefore, there is not necessarily any conflict between 4:15 and 24:2 as they are two separate conditions and offences. Whereas the offence in 4:15 could be an ill which affects the wider society (such as prostitution), the offence in 24:2 is simply restricted to personal immorality such as adultery or fornication and applies to both genders and attracts a specific punishment.
Just my humble opinion. Happy to stand corrected by a more cogent interpretation from the Quran and Arabic usage.