at a moment’s notice

at Preposition

— Used to describe where something is, or when saying something's position I am at home. Let's meet at the pub! — The time at which something happened or will happen Breakfast is at 9 o'clock. At 5pm we went home. — Indicating something's state At half price! Water boils at high temperatures.

at Symbol

— The @ symbol, used to replace at support@microsoft.com is an email address. Apples @ £1.50 per kilogram.

a Determinative

— A is used when the following word could be any of a certain type. Compare "A book I saw on the shelf" and "The book I gave you yesterday".

a Noun

— A is the first letter of the alphabet. The letter "a" comes before "b". — In some schools, an A is a very high grade. Ron got an A on his earth science test.

notice Verb

— If you notice something, you become aware of it. You didn't even notice that I cut my hair. When the cook changed, I noticed the difference right away. I've looked at her a thousand times, but I'd never noticed her green eyes before. "Did you see the mistakes?" "No, I'm afraid I didn't notice. I couldn't help noticing that you look lost. Can I help?

notice Noun

— when you notice something She asked for help, but they took no notice of her. When the changed were made, we didn't take much notice. The mistake escaped notice for almost three years. — A notice is a piece of paper with information or a warning. She sent us a notice about the change of dates. — Notice is information that you give to someone. The shop closed without any notice.