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The story

1. Proto-Germanic*tūmōną
2. Proto-West Germanic*tumbōn
3. Old Englishtumbian
4. Middle Englishtumben
5. Middle Englishtumblen
6. Englishtumble
7. Proto-Indo-European*legʰ-
8. Proto-Indo-European*légʰyeti
9. Proto-Germanic*ligjaną
10. Old Norseliggjader.?
11. Middle Englishlogge
12. Englishlog
13. Proto-Indo-European*bʰeh₂ǵosder.?
14. Proto-Indo-European*bʰeh₂g-der.?
15. Proto-Germanic*bōks
16. Proto-West Germanic*bōk
17. Old Englishbōc
18. Middle Englishbok
19. Englishbook
20. Englishlogbook
21. Englishlog
22. Englishtumblelog
23. English todayTumblr

From tumblelog, an early form of microblogs.