18 March] 1805 in Hapsal (now Haapsalu) – 29 December [O.S.
17 December] 1887 in Saint Petersburg) was an Estonian linguist who researched Uralic languages, mostly Estonian.
Wiedemann was also a botanist.
Wiedemann was of German-Swedish origin.
In 1869 he published an Estonian-German dictionary (Ehstnisch-deutsches Wörterbuch), which was the richest dictionary of Estonian words for a long time.