This is unexpected — in 1999 mathematician Mike Keith programmed a computer to generate knights’ tours using Warnsdorff’s rule and then labeled the successive squares A, B, C, etc. to see whether any 8-letter words emerged. After about a million tours, he found two, UNSHAVEN and ARCHIVAL:

M T Q B W D O F   E T W F G J Y H
R C L O P G X C   V E F Y X G T K
U N S H A V E N   S D U H U L I Z
D K P S H Y B U   D G Z K X M L S
Q V G J I T M Z   A R C H I V A L
H E R C F I L A   F C J W N I R M
W D G J Y J A L   Q B A D O P K B
F I X E B K Z K   B E P O J C N Q

After some further searching he also found PERORATE and EPIDURAL. See the link below for more results.

(Michael Keith, “Knight’s Tour Letter Squares,” Word Ways 32:3 [August 1999], 163-168.)