Bella is not only a short form of Isabella and other names ending in Bella, it can also be used as a short form of names beginning with the element Bel, ex. Belinda.
The name Bella can be translated, though far less commonly than the Italian translation, from the plural Latin for "war". (The singular is bellum.)
― Anonymous User 3/1/2015
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This name is linked to the Latin words 'bellum' (meaning 'war') and 'bellus' (meaning 'beautiful' or 'pleasant') - it is the plural of the former and the plural or feminine form of the latter. It's up to you which etymology you choose to believe, I suppose.
With a few alterations, Bella could mean "dawn" in Scottish Gaelic; beul an là (literally, "mouth/opening of the day"), so therefore, with some contractions, it could become "Beullà" or "Beulà" (both pronounced as "BAY-lah"). The literal meaning might not be so flattering, though.