Merry was a kind of butler to the king. It was customary to give such titles toFor the Saxon and Frankish kings from which, on whom the Rohirrim draw their inspirationwere inspired, it was customary to give such titles: butlersteward, stablemaster, stewardbutler. Butler means 'bottle"bottle-bearer'bearer", words very similar to holdwine.
Of course, in a royal court of a medieval king such a position implied much more than being a mere servant: they were positions that denoted being friends of the king and men of trust. Butler and steward came to mean ministerial positions.