Three-drop water radical on the left — the side-form of
水. Marks
没 as historically water-related: the original meaning under the mò reading was 'to sink, submerge, be drowned by water'. Same family as
沉 (to sink),
浸 (to soak),
淹 (to submerge). The everyday méi negation sense ('not, have not') is a much later semantic extension from 'gone, vanished beneath the waves'.