firsthand
adj.coming directly from your own experience rather than hearing about it from someone else. You use this to describe knowledge you gained by being there yourself.
adj.obtained directly from the original source or through personal experience. Often used attributively before a noun to describe evidence, knowledge, or accounts.
“She has firsthand experience of the problem.”
“The journalist provided a firsthand account of the events after spending three weeks in the conflict zone.”
“While textbooks provide a theoretical framework, firsthand observation of the chemical reaction in a controlled laboratory setting is essential for a complete understanding of the process.”
Typically placed before the noun it modifies; can also function as an adverb in the same form.
“He referred to this summer’s World Cup, which was co-hosted by the US, and the excitement it provided, adding, “Millions of people across North America experienced that passion firsthand.”
“I had an understanding, a firsthand understanding, of how people of color are treated, you know, because I knew that.”
From first + hand.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.