Merger
Etymology
From the verb "merge," from Latin "mergere" (to dip, plunge, or immerse). Two things immersed together lose their separate surfaces — an apt image for firms dissolving into one. The legal noun formalized the idea of businesses blending rather than one simply swallowing the other.
noun · /MUR-jer/
The combining of two companies into a single new entity, ideally as equals.
What it names
The union framed as partnership, so you can weigh the polite story against who really ends up in charge.
Example
The press release called it a merger, but within a year every executive from the smaller firm was gone.
Related idea
A merger is billed as two companies joining as equals into something new; an acquisition is one company plainly buying another. The line blurs on purpose — "merger" is often the gentler word for what is really a takeover.