Rashi on Exodus 30:25/רש"י על שמות ל׳:כ״ה

1רקח מרקחת A COMPOUND COMPOUNDED — רקח is a noun and its accent proves it, for it is on the first syllable, on the ר, so that it is a noun just as are רֶקַח in (Song 8:2) “I would cause thee to drink of the mixed wine (מיין הרקח)” and רֶגַע in (Exodus 33:5) “one moment (רֶגַע אחד)”, and it is not a participle like (Isaiah 51:15) “[I am the Lord] who stireth up (רוֹגַע) the sea”, or (Isaiah 42:5) “Who spreadeth forth (רֹקַע) the earth”, where the accent is on the last syllable. Any thing (ingredient) which is mixed with another so thoroughly that one becomes impregnated with the other as regards the smell or the taste is called a מרקחת.

2Thus רקח מרקחת (lit., a mixing of a mixture) means a compounding effected by skilled art and perfect mixing.

3מעשה רקח THE WORK OF A COMPOUNDER — רֹקֵחַ is the name given to a workman skilled in this matter.