寸陰 is read as すんいん (sunin) and means moment.
すんいん
sunin
いっすんのこういんかろんずべからず
there isn't a moment to be wasted
すんぽう
measurement
すんぜん
just in front of
すんか
moment's leisure
すんだん
cutting to pieces
すんげき
short play
すん
sun (approx. 3.03 cm)
すんぽうきにゅう
dimensioning
すんぶんたがわず
without the least difference
すんぶんたがわぬ
exactly the same
すんぶん
tiny bit
すんじ
moment