replica doesn't imply a power relationship. Master controls the slave , which is accurate

- Master database tells the slaves what to write

- Master clock tells slave the time

- Master HDD controls the computer , so indirectly controls secondary -- though in this case slave HDD is more auxiliary rather than subordinate (this terminology isnt used anymore anyway)

In any case, master/slave terminology is historical and generally unproblematic, except apparently in the US, but so many words are problematic for someone somewhere that it's not wise to go down that road