also: せきすん
noun
tiny thing; trifle; insignificant amount
Literally 'a shaku and a sun' (old units of length), used figuratively to mean something very small or trivial. Often appears in negative contexts or as a humble expression.
彼は尺寸の違いも見逃さない。
He doesn't overlook even the slightest difference.
尺寸の功績もない。
I have not even a trifling achievement.
From the old Japanese units of length 尺 (shaku, about 30.3 cm) and 寸 (sun, about 3.03 cm). The combination figuratively denotes a very small distance or amount.