adverb/tɑ̃.buʁ ba.tɑ̃/
eagerly; promptly, briskly, energetically
“mener une affaire tambour battant, mener une affaire rondement”
Synonyms: rondement
Literally, “beating [the] drum”, with the positioning of the present participle after its complement which was frequent in Old French (the modern French equivalent would be battant tambour). Compare chemin faisant, Belle au bois dormant.