We use another + a singular noun and other + a plural noun when both of them are used as determiners.

Example

  • I need another cup of coffee. (singular)
  • I want to talk to other doctors. (plural)

When discussing the second of two things, or the opposite of two things, we use the other + a singular noun (observe that there is the before other),

Example

  • This computer here is new.
  • Another computer is about five years old. ❌
  • The other computer is about five years old. ✅

Additionally, to refer to the remaining items in a group, we use the other + a plural noun.

Example

  • Joel and Karen are here, but where are the other kids?

References