There is a total of 85689 clues beginning with o
- Only US president elected under the Federalist Party
- Only US president to have his portrait on a coin during his lifetime
- Only US president to have three veeps
- Only US president whose surname is more than 50% vowels
- Only US president with a star on the Hollywood Walk of Fame
- Only US senator with a unit of measure named after him
- Only US state in which the name of the state and its capital share no letters: Abbr
- Only US state motto in Spanish
- Only US state whose flag isn't rectangular
- Only US state with a non-rectangular flag
- Only US state with a pennant-shaped flag
- Only US state with a Spanish motto
- Only US state with a three-word capital
- Only US state without a rectangular flag
- Only US vice president born in Maryland
- Only unanimous Baseball Hall of Fame electee
- Only unanimous Cy Young Award winner between Dwight and Randy
- Only unanimous inductee at Cooperstown
- Only ungulate that mates in the seated position
- Only United Nations member whose name starts with "O"
- Only US president to receive both a Purple Heart and a Pulitzer Prize
- Only US president with a star on the Hollywood Walk of Fame
- Only US state that can be typed on one row of the QWERTY keyboard
- Only US state with a diamond mine
- Only US state with two official languages
- Only US swimmer to compete in five Olympics
- ONLY US, HANS!: 1983
- Only valid three-letter Scrabble word that doesn't contain Y or any consonant
- Only Veep from Maryland
- Only veep to resign
- Only vegetable never sold frozen, canned, processed, or cooked
- Only vice president born in DC
- Only wants for sex, say
- Only way to get off scot-free?
- Only weapon in Clue that isn't metallic
- Only Welsh-born Batman
- Only what a person can take?
- Only Wimbledon champion to wear a wig
- Only Wimbledon winner to wear a wig
- Only winner of eight consecutive Norris Trophies
- Only winner of Indy, Daytona and LeMans
- Only winner of People's Sexiest Man Alive who's no longer alive
- Only winner of six straight European Figure Skating titles besides Sonja
- Only woman aboard the Argo, it's said
- Only woman to outwit Holmes
- Only woman to sing lead vocals on a Beatles song
- Only woman to win the top prize on "The $64,000 Question"
- Only woman with two Nobel prizes, formally
- Only word containing three consecutive pairs of double letters
- Only word heard in a 1958 song of the same name
- Only word spoken in Mel Brooks's "Silent Movie"
- Only word that's a two-digit number backward
- Only words on the front of the Great Seal of the United States
- Only work Michelangelo ever signed
- Only work of art that Michelangelo signed
- Only work that Michelangelo signed
- Only World Series perfect game pitcher
- Only X-rated film to win the Best Picture Oscar
- Only you
- Only You actress
- Only ___ a customer
- Only ___ a customer
- Only's companion
- Only's partner
- Only, in Bonn
- Only, in Bremen
- Only, in Germany
- Only, in Oberammergau
- Only, in Osnabruck
- Only, in Ulm
- Only
- Only: Fr
- Only: French
- Only: Ger
- Ono
- Ono from Tokyo
- Ono of "Double Fantasy"
- Ono of JAPAN
- Ono who co-founded Artists Against Fracking
- Ono's husband
- Ono's love
- Ono/Lennon album
- Onomastician's study
- Onomasticon's contents
- Onomastics study
- Onomatologist's study
- Onomatopoeia
- Onomatopoeia for sleep
- Onomatopoeia
- Onomatopoeic
- Onomatopoeic Black Eyed Peas hit of 2009
- Onomatopoeic cry
- Onomatopoeic dance
- Onomatopoeic drumbeat
- Onomatopoeic game on "The Price Is Right"
- Onomatopoeic mint name
- Onomatopoeic musical effect
- Onomatopoeic prefix
- Onomatopoeic Sinatra album title
- Onomatopoeic sound