Definition:

: former.

Examples: 

I was pleased to find an interview with the whilom president of my alma mater in the local paper.

“On the eastern side settlement and agriculture have all but obliterated the whilom tallgrass prairie, so that it is hardly visible to anyone who would not seek it out on hands and knees….” — William Least Heat-Moon, The Atlantic, September 1991

by MERRIAM-WEBSTER DICTIONARIES.