Answer: oh

AnswerCrossword Clue
ohOhio
oh(an exclamation of surprise, pain, sympathy, etc.)
ohed in direct address oh, waiter! Will you come here, please?
ohused to express an emotion (as surprise or desire) or in response to physical stimuli
ohed to express acknowledgment or understanding of a statement
ohed to introduce an example or approximation
ohto exclaim in surprise