Literally: it is another type of sleeve
Meaning: that’s a different kettle of fish; A whole other ball game
Origins: Attributed to the 16thcentury, the aristocrats didn’t have sleeves permanently sewn to their clothes so they could be interchanged to become a different attire. It is believed that during the tourney, knights would wear their lover’s color, a sleeve put on their shield or spear. Those sleeves were a symbol of their love and fidelity if they changed the sleeve that means their love had changed and proved their infidelity.
Later on, people used a half sleeve to go over the original sleeve and protect them, for example, clerks used to wear them. Another hypothesis is that in the 19thcentury, this expression would come from shop keepers and would mean that they needed to make a different item.
Examples : Ce ne sont ce jour d’hui que rêves, et ce qu’il adviendra de ces rêves, « c’est une autre paire de manches », comme dit notre ami et allié Brantôme : expression bizarre que je n’ai jamais ouïe que de sa bouche ni lu que sous sa plume, étant manifeste qu’on ne sait pas du diable ce que vient faire là cette « autre paire », la première n’étant pas en question. — (Robert Merle, Paris ma bonne ville, 1980)