那么
nàmo · HSK 2
so
那 (that) + 么 (suffix) = 'that-much' → so/then
那 means 'that' and 么 is a grammatical suffix forming adverbs of degree. Together 那么 literally reads as 'that-much,' used like English 'so' (so big) or 'then' (then let's go).
那 — 邑 radical 阝(right) + 冄 phonetic
Originally referred to a place name in ancient China, with the right-side 阝 (city/region radical) indicating a settlement and 冄 providing the sound. Over time it lost its geographic meaning and was borrowed as a demonstrative pronoun meaning 'that' or 'those'.