cf. Orus in Etymologicum Magnum 490.16.
The etymology offered for kapparis (already kappa 327) is almost certainly false. Greek mp is euphonic anyway, and it is highly unlikely that the nasal would assimilate to a voiceless stop and yield pp. This consonant cluster generally appears from contraction of compounds in which kata/ is the first component and the second begins with p- or in words for plants and animals.
As the word is the name of an indigenous plant, it is more likely to be a loan from the non-Indo-European peoples who inhabited the area before the Greeks.