the part of a sundial that casts the shadow used to indicate the time (the dial's pointer or style).

日時計で影を作り時刻を示す部分（日時計の指針・スタイル）

in geometry and number theory, an L-shaped figure or the piece added to a figure to form a larger similar figure; also the difference between successive figurate numbers (e.g. the odd numbers are gnomons that generate square numbers).

（数学）図形を大きくする際に加えるL字形の部分、または連続する図形数の差（例: 奇数が平方数を作るグノモンになる）