Tautology is putting extra words in a sentence which mean the same thing, so there is no point having them there. Newspapers, in their bid to pad a story out to a certain number of words, are the worst culprits, and you'll often see phrases like "illegal theft" (all thefts are illegal therefore the word illegal isn't needed), "dangerous speeding" (all speeding is dangerous), "dishonest politicians" (well, you get the idea…)
Here's a list of some real place names from around the world, which you can use as examples when you try to Win Friends and Influence People by telling them what tautology is (just before they punch you for being a smart-***):
River River River Avon, England - Avon, spelled Afon in modern times, is Welsh for river.
River River River Río Guadix, Spain - Río is river in Spanish, Guad river in Arabic and Ix is river in Phoenician.
Long Tidal River River Connecticut River, United States - Algonquin.
Big River River Mississippi River, United States - Algonquin.
Lake Lake Second Lake Rotorua, New Zealand - Many NZ lakes have the "Lake Roto-" form.
Lake the Lake Lake Tahoe, Nevada/California - Washo Native American Tribal language.
Lake Lake Lake Nyassa, Malawi/Mozambique - Yao.
Lakeville Lake Michican, USA - The village is Lakeville, the adjacent lake is Lakeville Lake.
Hill Hill Bredon, England - Celtic/Saxon.
Hill Hill on the Hill Breedon on the Hill, England - Celtic/Saxon.
Mount Mount Big Mount Maunganui, New Zealand - Maori.
Mount Snowy Mountains Sierra Nevada Mountains, California - Spanish.
Hill Hill Hill Hill Torpenhow Hill, England - SW-English, Celtic, Anglo-Saxon, English.
Hill Hill Hill Pendle Hill, England - "Pen" Cumbric language and the suffix "dle" from the Old English language.
Mountain Mountain Mongibello, Sicily, Italy - Latin "Mons" and the Arabic "Gebel".
Peak Peak Summit Peak, New Zealand - The US also has five hills called Summit Peak.
Sheep Islands Islands Faroe Islands, North Atlantic - Faroese.
Island Islands Gili Islands, Indonesia - Sasak.
Many Islands Islands Polynesian Islands, Pacific Ocean - Greek.
The The Tar Tar Pits La Brea Tar Pits, California - Spanish.
Deserts Desert Sahara Desert, Africa - Arabic.
Waterfall Waterfall Waterfall Eas Fors Waterfall on the Isle of Mull in Scotland
Beech Wood Wood Wood Beechhurst Holt Wood, England - Anglo-Saxon.
View View Elementary School Vista View Elementary School, Minnesota - Spanish.
Valley Valley Beqaa Valley - "Beqaa" is Arabic for valley.
The Rock of The Rock of Tariq The Rock of Gibraltar - Arabic.
Town's Town Townsville, Australia - French.
East East Timor-Leste, East Timor - Indonesian/Malay, Portuguese.
Circle Circle Trendle Ring, Somerset, England.