Thanks for all those helpful replies.
I did think of Zac, but thought that may have been short for Zachery?
Never thought about Ike, Iky etc, so there's a possibility.
Isaac is the only name.
Basically Isaac is my gg grandfather from England. His son, my g grandfather, William was born 1850's in England, and migrated to Australia. On William's Australian Marriage Cert his father is named Isaac, but on his Death Cert his father is listed as William. William's mother was listed as Elizabeth Lee.
The surname is Swindail, and that name has many variations. Over the last 10 years I've searched for any record of the birth of William, and his parents through BDM's, Censuses, and even had a RootsChatter visit Lancashire to view Parish records without success.
I've tried every variation to find William's birth and his parents, so was hoping this new idea might work. There have been plenty of "possibles", but never anything to confirm this family.
I really don't require any one to search further, as I think I've exhausted every variation/avenue open to me, but as a nickname for Isaac was something that just came to me, I thought I would give it go.
Thanks
Les