Etymology
Borrowed from Scots hiddle, from Middle Scots hiddill, from Early Scots hyddyll, an alteration, due to final s mistaken for the plural ending, of hyddlys (“hiding-place, concealment”), from Old English hȳdels (“a place of concealment, hiding-place, cavern, cave”), equivalent to hide + -le.
For loss of final s compare burial, riddle. More at hide, huddle.