Note that in some places it is a hyphenated word and others it is not!

• 02.113 and fitted it into the key-hole.
• 03.028 “He is too fat to get through key-holes yet!”
• 03.044 will shine upon the key-hole.”
• 09.014 at his keyhole.
• 11.014 nor any sign of bar or bolt or key-hole;
• 12.100 No trace of a keyhole was there left on the inside.

OED gives “keyhole” – one word – but the hyphenated form is in the example texts.

“keyhole, n.” OED Online, Oxford University Press, June 2017, http://www.oed.com/view/Entry/103145. Accessed 14 September 2017.