Apparently from 'abal through the idea of negation; nay, i.e. Truly or yet -- but, indeed, nevertheless, verily.
see HEBREW 'abal
2 in late Hebrew as a decided adversative, howbeit, but Daniel 10:7, 21; Ezra 10:13; 2 Chronicles 1:4; 19:3; 33:17 (compare Arabic of a truth, sometimes, from the context, nay rather Qor 2:82; 2:94; 2:110; 2:129; 2:149; 2:165; 2:261; 3:143; 4:52 etc.)
III. אבל (compare Arabic able to manage camels, from , collective, Sabean אבל camel DHMZMG 1883, 329). On this etymology, form ׳אוֺ needs explanation; GFM (privately) queries whether, if Genuine, name may not be theophoric (x + £l), possibly error for אַדְבְּאֵל; or Aramaic Aph`el from יבל (which in any case may have influenced pronunciation).