AFAIK, "enemy combatant" is the extent of the term used, and it connotes a status that can be used (but is not necessarily used) to keep a person out of the apparatus we know as Article III Courts.
Or put anther way, all enemy combatants are subject to incarceration and punishment by the capturing government.
I'm curious what you envision as a "legal enemy combatant," in contrast to your proposed label, "illegal enemy combatant."
>> How about as an ILLEGAL enemy combatant,
Aka, unlawful enemy combatant
> I'm curious what you envision as a "legal enemy combatant,"
Someone who is both in uniform, and an enrolled
combatant on behalf of a state that is a signatory
to applicable Conventions, neither of which applies
to members of the Cutthroat Cult.
In wars past, these folk (e.g. spies, infiltrators)
were subject to summary execution.