One has no opinion or preference about something. ("Ain't" is a nonstandard contraction that is considered very informal.) A: "Where do you want to go for dinner?" B: "Wherever you want. I ain't particular."

To act as one would in one's particular profession while in a different setting. Bobby, I know you're off duty, but can you please wear your doctor's hat for five minutes and tell me what's wrong with my arm? I don't want to have to go to the hospital. My wife was still wearing her judge's hat when she tried to intervene with our neighbor's arguing kids.

To laugh in a particular manner. I couldn't help but chuckle with delight when I saw the little girl feed her ice cream cone to her dog.

dated A euphemism for the thick, brown, sometimes lethal fog caused by air pollution in London, especially during the 19th and early 20th century. For many older citizens living London during that time, they could as easily be killed by a London particular as by an attack from a criminal.

Specifically. Is there anything else in particular you hoped to do on your trip here? Dad did mention something in particular, I just can't remember what it was.

The specific, important details or finer points of something. He wanted to schedule a meeting so we could go over the particulars of the deal. Just let me know what the particulars are and I'll see if I can help.