@PenyafortSince we find “matar” in Romance languages of the Iberian Peninsula but not in other Romance languages, it’s not unreasonable to suspect that the Catalan verb came from Arabic, either directly or via Spanish.
It is not impossible. But I wouldn't say it's that reasonable either.
As I've said, first, Arabisms are usually nouns and adjectives, not verbs. It probably has to do with the nature of it. For this to come from Arabic, we'd have to accept that a past tense was taken as a root (since, correct if I'm wrong, the vowel wouldn't be a 'long a' in the present tense), and also accept that 'to die' changed its meaning into 'to kill'. There's also a common connection between 'to kill' and 'to turn off, put out' in
matar (matar el llum, matar el fuego...) that can also be seen with those coming from
tutare (
tuer le feu/la chandelle in regional French,
tudar la flama in Old Catalan,
atudar/tuar lo fuòc in Occitan), so that a parallel can be set which I'm not sure if it exists in Arabic.
Secondly, massive contact between Catalan and Arabic (or between Catalan and Spanish) was rather posterior to the first attestations of the word. A much higher number of forms of it in Western Catalan might have hinted into an Arabic origin, but as far as I know it doesn't seem to be the case.
Thirdly, the word can be found at least in Occitan. We could also speculate whether other terms, like those derived from
mat(t)us in French and Italian, are also related. And a Latin *
mattare, either from
mactare or from
mattus, is a perfectly plausible origin.
I never rule out any possibility, etymology can be crazy sometimes, but I tend to adopt the most logical among the several proposals given, aside from developing a certain feeling about what may be more sensible through the years. In some cases the very fact of having two options concurring actually reinforced the existence of a word.