To know of something firsthand means the information is obtained from the original source or from personal experience. Firsthand may be used as an adjective to explain the type of information that has been acquired or as an adverb, explaining how the information was acquired. Firsthand is the preferred spelling in North America, first-hand is the preferred British spelling, either spelling is correct.
Secondhand refers to information or knowledge that is not from the original source and may be used as an adjective or an adverb. Secondhand information is relayed through a middleman. The preferred British spelling is second-hand. Secondhand may also refer to clothes or other goods that have been previously used.
Thirdhand refers to information or knowledge that is quite far removed from the original source and may be used as an adjective or an adverb. The preferred British spelling is third-hand.
Fourth-hand, fifth-hand, etc., are exaggerations of the concept of thirdhand information and are always hyphenated.
Examples
Jolie then called on the United Nations Security Council to send its ministers and ambassadors to witness the crisis firsthand. (UPI)
Now in his sixties he learnt first-hand how much fun you can have exploring New Zealand as he traced the footsteps of where the new tour will take its first guests. (The Sunshine Coast Daily)
We’ve heard first-hand from pension funds that these emails spark important internal discussions,” she said. (The Guardian)
Reach Healthy Communities will use a new grant to help reduce secondhand smoke exposure among children. (The Republic)
A CHANCE visit to a second-hand store in Brisbane has led to treasured military memorabilia being returned to Rockhampton. (The Morning Bulletin)
Don’t permit smoking in your home and car, where recirculating particles give off thirdhand smoke long after the visible smoke is gone. (Lexington Herald-Leader)
He only has third-hand information and doesn’t know any more than what the media has been reporting,” the source reportedly said, on Gordon’s release from rehab. (International Business Times)