aplomar

In construction, to make something perfectly vertical/plumb (aplomar una pared). Reflexively, aplomarse means to gain composure or self-assurance — to become steady and serious, the opposite of nervous or flustered.

• El albañil aplomó la pared antes de seguir levantándola. — The bricklayer plumbed the wall before continuing to raise it.
• Con los años se ha aplomado mucho. — Over the years he's become much more composed.
• Tardó unos minutos en aplomarse antes de hablar en público. — It took him a few minutes to gain his composure before speaking in public.

Confusing the reflexive aplomarse (to gain composure/steadiness) with the literal construction sense — outside a building context, aplomar is almost always about a person's demeanor, not a wall.