私下
sīxià · HSK 7
in private
🔒 私 (private/personal) + 下 (under) = kept under privacy, done privately
私 carries the sense of private or personal, and 下 means under or below; together they point to matters handled under wraps, away from public view — privately or in secret.
下 — horizontal line 一 + mark below
下 is an indicative character: a long horizontal line represents a reference level, and a shorter stroke placed beneath it points to the area below. The original meaning 'below, down' comes directly from this spatial diagram, and it later extended to verbs like 'descend' and 'lower'.