'Bowl' is not onomatopoeic. The word 'bowl' means 'bowl' because it is the name of a thing, not because of the sound it makes, (unless he is talking about glass bowls which have a tendency to smash if dropped, which would bring about onomatopoeia). Onomatopoeia only happens with 'sound/action' words, like itch, screech, crash, splat, smash, rip, zip, stab, thud...

I have just had a squint at my old friend the etymology dictionary, and discovered that the verb 'bowl' comes from Latin, 'bulla' (bubble), via Old French, 'boule', and the rounded vowels are present here too, which suggests roundness.

I do know what Rich is getting at, but I can't remember the word for it :s All languages have examples of this, where vowels are used to indicate shape and/or size = wide/thin (long /i/ compared to short /i/), little/grand (short /i/, long /a/)...