This site suggests that òliba comes from uwwila, which seems onomatopoetic to me. For xibeca, I've got nothing, except the probably wrong association with xebec, which almost certainly comes to us from Catalan, from the Arabic, to entwine or fasten. I'm wandering rather far down the primrose path of dalliance with false etymologies here, but possibly some link to the predations of an owl?
