What does 1ce stand for?

Once

1ce is an abbreviation for "Once," which is typically used in text messages and online. It combines the pronunciation of the number 1 and "ce" to create the sound of "once." The abbreviation may be more confusing than helpful because it's not very clear how it's supposed to be pronounced. Since it may be confusing for most people and it barely saves time over typing "once" it's probably not worth using.