FWIW here is a list of schools with nicknames that don't end in "s."

Syracuse Orange
Stanford Cardinal
Cornell Big Red
Dartmouth Big Green
Presbyterian Blue Hose
William & Mary Tribe
Alabama Crimson Tide
Illinois Fighting Illini
Marshall Thundering Herd
Massachusetts Minutemen
Navy Midshipmen
Nevada Wolf Pack
NC State Wolfpack
Notre Dame Fighting Irish
Tulane Green Wave
Tulsa Golden Hurricane
North Texas Mean Green
Rhode Island College Anchormen
Millikin Big Blue
Bucknell Bison
Howard Bison
Bethany Bison
Gallaudet Bison
Nichols Bison
North Dakota State Bison
Oklahoma Baptist Bison
Hampshire Black Sheep
Wellesley Blue
Simon Fraser Clan
Cedar Crest Clan
Harvard Crimson
Central College Dutch
Union College Dutchmen
Southeastern Fire
St Louis CC Fury
Centenary Gentlemen (men's teams only)
Xavier (NO) Gold Rush (men's teams only)
UBC Okanagan Heat
Vermilion Ironmen