大層
たいそう · taisou · JLPT N2 · adverb
very much
大層 = 大 big + 層 layer: a big stack of degree, so very much or greatly
層 means layer or stratum, and 大 (big) stacks onto it, so the degree piles up high. It is a formal, somewhat old-fashioned intensifier, as in 大層立派 (very splendid).
大 — pictograph of a person with arms outstretched
大 is a pictograph showing a person standing with arms and legs spread wide. The outstretched arms suggest 'big' or 'great', extending from the literal image of a large stance to abstract meanings like important or grand. It is one of the oldest characters, found on oracle bones.