measurement, tenth of a shaku, a little, small
寸 centers on a small unit of length, roughly an inch, and by extension anything small or a little bit. The measurement sense is the root, and the idea of smallness grows naturally from that.
寸 is a pictograph of a hand with a mark indicating the pulse location, which was used as a unit of measurement (the distance from the wrist to that point). Over time it came to represent a small length and, by extension, smallness.
The shape looks like a hand with a small mark near the wrist. Picture measuring a tiny distance from that mark: 寸 is a small measurement.
For スン, imagine measuring something and saying 'soon' it will be exactly one sun (寸): soon -> スン, a little unit of length.
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sun (approx. 3 cm)
just before; on the verge of; on the brink of
measurement; size; extent; dimension
one sun (approx. 3 cm)
short play; skit
cutting to pieces; tearing to pieces
taking measurements
actual size; full size
actual size; exact size
cylindrical
tiny bit
dwarf; midget; elf; Tom Thumb; Jack Sprat
brief review; brief comment
long nail; spike
a bit more; a bit longer
font size
slight; minor; trifling; trivial; petty
there isn't a moment to be wasted; every moment is precious; make hay while the sun shines
tread on a worm and it will turn; even a tiny bug will defend itself; even the weakest and smallest beings have their own wills, so do not make light of them
an inch ahead; the immediate future