sliver
A very thin, small piece or slice of something.
A sliver is a very thin, small piece of something, like when you cut a tiny wedge of pie because you're too full for a normal slice, or when a thin fragment of wood gets stuck painfully under your skin.
The word captures that sense of something narrow and sharp-edged. You might eat just a sliver of cake, take a sliver of soap to wash your hands, or see a sliver of moon in the night sky when it's just a thin crescent.
Slivers of wood are especially notorious: when you run your hand along rough lumber or an old fence, these tiny wooden needles can pierce your skin. They're small but surprisingly painful, and getting one out requires patience and tweezers (or sometimes an adult's steady hand).
The word suggests something delicate and precise: a sliver of light coming through a barely-open door, a sliver of doubt creeping into someone's confidence, a sliver of hope when things look difficult. In each case, it's just a small amount, but sometimes that thin slice is exactly what matters.