The best replacement for admin is moderator.

The best alternatives to admin are rated as following:
★★★★★  moderator
★★★★  administrator
★★★  mod
★★  power user
★★  root
★★  domain admin
★★  secretary
★  user
★  system admin
★  hacker
★  console
★  admin
★  wheel
★  op minecraft
★  network admin
★  officer facebook
★  standard user
  amx
  op
  public admin
  enterprise admin
  database admin
  725
  local admin

Your alternative for admin is not listed? Suggest!
Speaking about admin, one probably shouldn't forget about cmd.

Other search terms related to admin and their ratings are:
★★★★★ cmd
★ python
★ command prompt
★ client
cheat engine
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Google Trends

Scale is based on the average worldwide traffic of admin in all years. Click on graph for more.
admin
moderator
administrator