Definition of slow to:
(n) :
a broad, flat, wooden bar, a
slat, especially as used to secure a door, window, etc; a metal bolt or wooden bar, especially as a
crosspiece
"1819: "One is from Hexamshire; he is wont to trace the Tynedale and Teviotdale thieves, as a bloodhound follows the slot of a hurt deer." -- Walter Scott, Ivanhoe"
(v) :
to bolt or lock a door or window