1. muscle; tendon; sinew
この肉は筋が多くて硬い。This meat is tough and full of sinew.
2. vein; artery
3. fiber; fibre; string
4. line; stripe; streak
光の筋が走る。A streak of light flashes across.
5. reason; logic
それなら一応、筋は通ります。In that case, it makes sense, at least in principle.
6. plot; storyline
話の筋が少しずつ分かってきたぞ。I'm starting to understand the plot little by little.
7. lineage; descent
他国の王族筋も招く予定だよ。We also plan to invite royalty from other countries.
8. school (e.g. of scholarship or arts)
9. aptitude; talent
10. source (of information, etc.); circle; channel
ある筋から聞いたんだけど。I heard it from a certain source, but...
11. well-informed person (in a transaction)
12. effective move; logical move; suji; tesuji
13. ninth vertical line
14. seam on a helmet
15. gristly fish paste (made of muscle, tendons, skin, etc.)
16. social position; status
17. on (a river, road, etc.); along
18. counter for long thin things; counter for roads or blocks when giving directions
19. street (in Osaka)
20. (Edo period) counter for hundreds of mon (obsolete unit of currency)