"Metronome" is not a foreign word, like "cat" or "car." it is an invented name for an invention, given by the inventor (Johann Maelzel) in 1815. Since then, the name has been adopted and used in every language, with various spelling patterns, depending on the phonetic system in each language. For instance, in some languages, the final e is dropped; in some other languages, an accent may be added; and so on. There is no need to clutter the Arabic language with a new name for this device when the universally accepted name will do.

Incidentally, the invention seems to have been copied and developed from an earlier invention by Dietrich Nikolaus Winkel, who apparently did not protect his invention. Winkel called his instrument "chronometer."