Midsummer Eve

noun Chiefly British.

the evening preceding Midsummer Day: formerly believed to be a time when witches and other supernatural beings caused widespread mischief.

Origin of Midsummer Eve

late Middle English word dating back to 1400–50

Also called Midsummer Night, St. John's Eve, St. John's Night.

Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

As I stood gazing around me I remembered it was Midsummer-eve.
Farthest North
Fridtjof Nansen
Midsummer-eve, when the days are longest and the nights shortest, was now come.
The Fairy Book
Dinah Maria Mulock (AKA Miss Mulock)
It was then one o'clock, and midsummer-eve, the very time that twelve years before John had gone down into the hill.
The Fairy Book
Dinah Maria Mulock (AKA Miss Mulock)