AMERICAN IDIOMS STARTING WITH O
Odd man out:
An unusual or atypical person (or thing). ex. "In a high school where everyone was tough, I was the odd man out."
Off-color:
Rude. Vulgar.
Off-duty:
Not working at one's job. ex. "the policeman couldn't help me because he was off-duty."
Off the air:
No longer on TV (or the radio). ex. "They took that show off the air in November because nobody watched it."
Off the hook:
No longer having to do something, no longer blamed or under suspicion. ex. "Ok, you're off the hook. Your brother says he'll clean the bathroom."
Off the record:
Unofficially.
Off the top of one's head:
Spontaneously. Without thinking too much. "How many cafes are there in this town? Off the top of my head I can think of about 6."
On one's mind:
Occupying someone's thoughts. Being thought about. ex. "You were always on my mind."
(To do something) on one's own accord:
Willingly, without anyone forcing one to do something. "Did you make him apologize? No, he did it on his own accord."
On second thought:
Having given something more thought. ex. "On second thought, maybe you should sell your house and move into an apartment."
On the go:
Busy. Moving around busily. ex. "Jim is always on the go. He can never find time to talk to me."
On the house:
Something that is given away free by a merchant. "How much for the apple? Don't worry - It's one the house!"
On the loose:
(Most often used speaking about criminals) - free; not captured; "The bank robbers are still on the loose."
On the tip of one's tongue:
About to be said. Almost remembered.
On the wagon:
Not drinking alcohol. ex. "Hey let's go out for a couple of beers tonight. I can't - I'm on the wagon."
Once in a while:
Occasionally.
Other side of the tracks
The poorer part of a town.
Out cold:
Unconscious. ex. "The boxer was out cold."
Out of sorts:
Not quite oneself; In a bad/strange mood. ex. "Tom has been out of sorts recently."