The story
From a- (“in, on”) + building (“the act or process of building”).
First known use, by meaning
- First attested in the mid 16ᵗʰ century. Being built or under construction, as a structure or a vessel.
- First attested in the mid 16ᵗʰ century. Developing or arising, as a trend or an idea.
Etymology from Wiktionary, CC BY-SA 4.0.