一筋
ひとすじ · hitosuji · JLPT N1 · noun
line
一 — single horizontal stroke
一 is one of the simplest pictographs in Chinese, depicting a single horizontal line to represent the number one. It has retained essentially the same form since oracle bone script over 3,000 years ago. By extension it also means 'first,' 'whole,' or 'same.'
筋 — bamboo 竹 + flesh 月(肉) + strength 力
A semantic compound: 月 (flesh) shows it relates to the body, 力 (strength) hints at muscular force, and 竹 (bamboo) suggests fibers like bamboo strands. Together they depict the sinews or tendons that give the body its strength.