adunar

A literary, somewhat old-fashioned verb meaning to unite or join together — largely displaced by unir and juntar in everyday speech. Shows up mainly in formal or poetic writing.

• El tratado buscaba adunar los esfuerzos de ambas naciones. — The treaty sought to unite the efforts of both nations.
• Los poetas adunaron sus voces en un solo canto. — The poets joined their voices in a single song.
• Es difícil adunar intereses tan distintos. — It's difficult to unite such different interests.

Reaching for adunar in everyday conversation — it reads as stilted or archaic; unir or juntar is what a native speaker would actually say for 'to bring together' in ordinary contexts.

Often confused with unir.