Homophones o, oh, ooh, owe

o / oh / ooh / owe [oʊ/ǝʊ/o] 

o – exclamation & n. – exclamation – used to express strong emotion; n. – 1. 15th letter of the English alphabet; 2. zero or nought in specific discussions such as reading certain years i.e. 1903; 3. chemistry, symbol for oxygen

oh – n. & interj. – 1. number zero; 2. expressing surprise, resignation, pain, entreaty etc.

ooh – interjection & v. – interj. – expressing surprise either positive or negative – enthusiasm or displeasure; v. utter such an interjection

owe – v. – to be under obligation to or in debt to a person or thing