If "register" means to record or formally enter something:
* Unregister: This is the most direct opposite, meaning to remove something from a record.
* Ignore: This suggests not paying attention to something and thus not recording it.
* Overlook: Similar to ignore, this implies not noticing something worthy of recording.
* Forget: This means to lose track of something, suggesting a failure to register it in memory.
If "register" means to show or indicate something:
* Conceal: This means to hide something, the opposite of showing it.
* Disguise: This means to change the appearance of something to make it unrecognizable, preventing it from being registered.
* Mask: Similar to disguise, this means to cover something up, preventing it from being registered.
If "register" refers to a cash register:
* Pay: This is not a direct opposite but refers to the action that is usually performed with a cash register.
* Withdraw: This suggests taking money out of a register, the opposite of adding to it.
Ultimately, the best antonym depends on the specific context in which "register" is being used.