This character is a fusion of two characters which were separate in small seal script.
甾 of this sense was 𠙹 in the small seal script (古文/ancient variant 𠙾 in the Shuowen Jiezi), with three vertical straight strokes on top, representing the pictogram (象形) of a vessel (缶) made of clay: Xu Shen says 東楚名缶曰甾。象形. This became the current form in the clericalscript. "Zi" was the name used in Chu to call this kind of vessel.
This glyph was used as 載 (OC *zlɯːs) or proper nouns in oracle bone script.
The glyph of this sense is composed of 𡿧 (“calamity”) and 田 (OC *l'iːŋ, “field”). This glyph is also used as an alternative form of 災 (OC *ʔslɯː). It can be seen in the lower part of 葘.
This character was practically obsolete before it was revived as a modern translation for steroid. It is also a pictogram (象形) in this sense; the upper part represents the three side chains on the ring system, and the 田 component represents the tetracyclic core of steroids. See the image on right.
Smith (2011) interprets the oracle bone glyph as depicting the new moon and proposes that it originally wrote a word *ts[r]əʔ "darkened phase" i.e. "new moon", related to 緇 (OC *tsrə) "blackened", 菑 (OC *tsrə) "field cleared by slash and burn", 淄 (OC *tsrə) "murky (water)". Lunar meaning is also present in 臘／腊(là) of which this character is the upper-right component.