Fancy meeting you here!
“Encounter” can be used as a verb and a noun. As a noun, it came into English in the late 13th century, according to the Online Dictionary of Eytomology.
The dictionary also notes that the word originally meant a “meeting of adversaries.” It was created from the Latin “in” and “contra,” meaning against.
Though still used in an adversarial sense, the noun nowadays can also mean a surprise meeting.