どうも
どうも · doumo · JLPT N5 · expression
Thank you
dou (how) + mo (ever) = however you try; short for doumo arigatou
Built from dou (how) plus mo (even/ever): in whatever way, hence somehow or no matter how one tries. As thanks it is a clipped doumo arigatou, literally very much thanks, with the thanks left unsaid.