甾 is a modern chemistry term coined for the steroid ring (it stacks three 田-like rings under one 巛 top). An old, now rare reading zī named an ancient wine pot and a river, but you will only meet the chemistry sense today.
The three curved top strokes look like the stream graph 巛. In the modern chemistry coinage they are read as the three fused carbon rings sitting on top of the fourth.
田 here is not a real field. Its boxed grid was borrowed as a picture of the bottom ring of the four-ring steroid skeleton, giving the whole character its chemistry meaning.
