hi

The word “hi” means a friendly, casual greeting. In plain terms, the everyday, casual way to say hello.

“Hi” is pronounced heye (/haɪ/ in IPA).

Here is “hi” used in a sentence: “Hi, how are you doing?”

“Hi” is an interjection.

The word “hi” dates back to around 1800. Recorded in American English from the mid-1800s, likely a variant of the older greeting/attention-call "hey.".

“Hi” is a very common word in modern English, usually learned at around the A1 level.

Both are greetings, but 'hello' is more neutral and works in formal and informal settings, including answering the phone. 'Hi' is warmer and more casual, better suited to friends, colleagues, and relaxed situations. In a job interview you might say 'hello'; with a friend, 'hi' feels more natural.

'Hi' is informal. It is friendly and relaxed, ideal for people you know or casual conversations, and it is fine in most everyday emails today. For very formal or first-contact situations — a cover letter or a message to a senior stranger — 'hello' or 'dear' is a safer choice.

Both are casual greetings, but 'hey' is even more informal and familiar than 'hi.' 'Hi' suits almost anyone you are on friendly terms with. 'Hey' works best with people you know well and can sound too casual, or even abrupt, with strangers or in professional settings.