Denshi Jisho — Online Japanese dictionary

背筋 せすじ 1: the muscles along the spine; dorsal muscles;
2: spinal column;
3: seam in the back; back seam
Common word, Noun 
背筋 はいきん 1: the muscles along the spine; dorsal muscles;
2: spinal column;
3: seam in the back; back seam
Noun 
背筋鼠 せすじねずみ striped field mouse (Apodemus agrarius)
Noun, Usually written using kana alone 
背筋力 はいきんりょく strength of one's back
Noun 
背筋を伸ばす せすじをのばす to straighten up one's back (e.g. stand up straight, sit up straight); to hold one's head high
Expression, Godan verb with su ending 
背筋が寒くなる せすじがさむくなる a chill runs down one's spine
Expression 

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