Today's The Guardian quick crossword has "espied" as the answer to 16 down, clued as "spotted". Having never really seen this word used before, I'm curious as to how it differs from the word "spied".
"Spy" has one meaning (to infiltrate the enemy to gather information) which, as far as I can tell, "espy" lacks. However, the other meaning, to spot, seems to be shared between the two.
Is there a situation where it's more correct to use "espy" than "spy"? Or has "espy" been relegated to the realms of archaic English?