Wick, Pencil Lead, Marrow
Noun
しん
お買い得だったので、HBのシャー芯を百ケース買いました。
I bought one hundred cases of HB mechanical pencil lead because they were at a bargain price.
The kanji means wick and this word also means wick, but it means things at the core of other long things more often. Things like pencil lead and marrow.
The reading is the same as the one you learned with the kanji.