The most likely reason is someone created that Halloween font by starting with Gill Sans and modifying it. They then didn't change all of the internal names (the ones all OS's actually use) and is conflicting with the real Gill Sans font.
Disable the Halloween font. If the real Gill Sans suddenly returns, that's the problem. The Halloween font is junk.
Thanks for the reply.
Gill Sans MT is missing from MS Word 2004 font pull down menu, but when typed in it appears.
Whilst searching my system for font that match what has has replaced. I saw similar,yet different font called 'Dripping Marker'. I type the word "dripping" only into MS Word and it came up with Gill Sans MT.
I cannot see either Gill Sans MT or a font called Dripping on my system a this point using Finder or Font Book.
Do you have any suggestions on how to restore the 'Gill Sans MT' font back?
Below is an image of the Fonts.