Commentary for Genesis 41:43

במרכבת המשנה means — the chariot second in order to his chariot — that which drove next to his own.

‘B’MIRKEVETH’ (IN THE CHARIOT) ‘HAMISHNEH.’ I.e., in the chariot second to his own chariot, which travelled next to his own. Thus the language of Rashi.
Now according to this interpretation, the word hamishneh refers to the noun, [“chariot,” meaning that this was the chariot of second rank]. The same applies in the verses: the priests ‘hamishneh’ (of the second order);⁶⁷II Kings 23:4. ‘eth mishnei’ (a copy) of this Torah.⁶⁸Deuteronomy 17:18.
The correct interpretation is that the word mishneh is adjectival,⁶⁹Meaning that this was the chariot of the mishneh, of he who was second in rank. just as: And I shall be to you ‘l’mishneh’ (as a second one);⁷⁰I Samuel 23:17. For Mordecai the Jew was ‘mishneh’ (the second) unto king Ahaseurus.⁷¹Esther 10:3. Similarly, the expression, keseph mishneh,⁷²43:12. (the money of the mishneh) is adjectival and is to be understood as “the money of the ‘second’ purchase.” Now the grammarians⁷³Reference is to R’dak who mentions this point in his Sefer Hashorashim (Book of Roots), under the root shana. have already brought a proof to this thesis⁷⁴That the word mishneh here, and in the other three cases mentioned, (see Notes 70-72), all have the meaning ascribed to them by Ramban. since in all these cases the letter nun in the word mishneh is vocalized with a segol, [which does not indicate the construct state as would tzeirei], while mishnei hatorah⁶⁸Deuteronomy 17:18. and all nouns are vocalized with a tzeirei, as is the rule in the construct state. The sense of the present verse is that the king had a chariot known to be his, even as it is said, And the horse which the king rideth upon,⁷⁵Esther 6:8. and there was another chariot known to be for his second in rank, and another one for the third in rank.

במרכבת המשנה, a horse or mule especially designated for the King’s second in command to ride on.