an intimate or close friend; best friend
With a boon companion, she followed her new path.
a very close friend
She is inseparable from her boon companion of 20 years.
1566; boon from Fr. bon, lit. 'good fellow'
While speaking or rather hissing those words, the boon companion underwent much such a change as one reads of in fairy-books.
This dog, his boon companion, he would present to the Crown Prince.
It flashed upon her that this man—Roxdal's boon companion—must know far more than he had told to the police.
He drank enormous quantities of brandy, and was a boon companion of Coupeau.
It was from his boon companion, Egremont, who was doing Long Branch.
Leastwise, he ain't what you'd go so far as to call a boon companion.
Ikey was ready to meet them more than half way, and before long became their boon companion.
It is your pride to have been their associate and boon companion.
He was quite a boon companion, and had a marked objection to retiring to rest before daylight.
He was not only the boon companion of princes, but he was the prince of boon companions.