contextuar

A rare, technical verb from documentary and archival studies meaning to validate or support a claim using textual evidence — essentially, to back something up with a written source. It's specialist vocabulary, not something a general learner will encounter outside academic or archival writing.

• El historiador contextuó su hipótesis con documentos de la época. — The historian backed up his hypothesis with documents from the period.
• Es difícil contextuar esa afirmación sin fuentes primarias. — It's hard to substantiate that claim without primary sources.
• El archivista contextuó cada pieza con su ficha correspondiente. — The archivist supported each item with its corresponding record.

This word is specialist and rare — a learner will get far more mileage from respaldar (to back up/support) or fundamentar (to substantiate) for the everyday idea of backing up a claim with evidence.

Often confused with fundamentar.