Any difference between engine and machine?

Hi,

I have got a review of the Danish translation of Xboard to make sure of 
its quality. There is one point in the review that I would like bring up 
here. The reviewer asks if the terms "engine" and "machine" are used as 
synonyms in the source, and if so suggests that I translate both words 
with the same Danish term.

Is it true that "engine" and "machine are synonyms in Xboard?
If yes, I suppose it should be changed.
If no, would you please explain the difference to me?

Machine is used in these translation units:

Machine White / Machine Black / Two Machines (in Mode menu)
MachineWhite / MachineBlack / TwoMachines mode requires a chess engine
MachineWhite / MachineBlack / TwoMachines mode does not work with ICS mode
Illegal move "%s" from %s machine
Machine accepts your draw offer
Machine offers a draw
Machine Match

Regards,
Byrial Jensen, Danish translater