Learn English – Middle English for ‘Hello’

The Middle English equivalent for 'hello' was hail.

Origin of hail: Middle English from the obsolete adjective hail ‘healthy’ (occurring in greetings and toasts, such as wæs hæil see wassail), from Old Norse heill, related to hale and whole.
[Lexico]

Where Does 'Hello' Come From?

It may be true that OK is the most spoken word on the planet, but hello is a good candidate for the English word that most people learn first. The word is so ubiquitous that it’s surprising how new it is: hello has only been in use for about the last 150 years of the 1000-year history of English.

An older term used for greeting or salutation is hail, which dates back to the Middle Ages but was still in use in Shakespeare’s time; he used it both as a greeting (“Hail to your grace“) and as an acclamation (“Hail, Caesar!”). Interestingly, this word is related to others that originally meant “health,” such as hale, health, and whole. Since hail was presumably sometimes shouted (from a horse, across a river, from a tower), it isn’t surprising that several variants are recorded, including hollo, hallo, and halloa. Another variant of this interjection has subsequently had a long life as a noun and verb: holler.

[Merriam Webster]

From Speech Acts in the History of English:

For Middle English, Early Modern English and Modern English the MED and the OED were searched for the senses "greeting", "salutation", "welcome", "hello" and "how are you"........ The only Middle English daughter forms of OE hal can be found in the following 1225 OED quotation, where it occurs as an interjection:

(3) Hoal ði godnesse!
hail thy deity
Hail to thy deity!*

Lee Ballentine in an article on Quora wrote:

In medieval England, Hail fellow was a common greeting. By the 16th century this had morphed a bit into the more elaborate form "Hail fellow, well met." "God save you" would also have been a conventional greeting.

From The Saturday Evening Post:

Hello is a greeting that is understood almost everywhere in the world, but it hasn’t always been so. In fact, hello is a relatively young word, dating only back to 1827 according to the Oxford English Dictionary.

Before that, all the way back to the Middle Ages, hail was a common English greeting. (The word is related to health, so it was not only a salutation but well-wishing.) Through the combination of dialects, accents, and the lack of an authority on English spelling, a number of variants of hail developed over the centuries, including hollo and hallo. But even into the 19th century, these words weren’t used as greetings, but to indicate surprise or to attract someone’s attention — much in the same way we use hey and yoo-hoo today.

Another equivalent was Good morrow/morning.

According to Hobby Lark:

How to Speak at a Renaissance Faire

Greetings and Goodbyes
Good day -> Hello/Good morning.
Good morrow -> Hello/Good morning.
Well met! -> Nice to see you!
How met! -> How are you?
Farewell -> Goodbye.
I bid thee farewell -> Goodbye.
Anon -> I will see you later.