Music term: the first note of a scale, or the central key of a piece.
この曲の主調はハ長調です。
The keynote of this piece is C major.
main point; predominant element
General use: the most important or central element of something.
彼の演説の主調は環境保護だった。
The main point of his speech was environmental protection.
keynote; tonic
Compound of 主 (main) and 調 (key, tone). The musical sense is primary; the general sense is an extension.