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Definition 2024

Family relations and loyalties are stronger than relationships with people who are not family members.
- 1866, Anthony Trollope, The Belton Estate, ch. 30,
  Blood is thicker than water, is it not? If cousins are not friends, who can be?
- c. 1915, Lucy Fitch Perkins, The Scotch Twins, ch. 5,
  The old clans are scattered now, but blood is thicker than water still, and you're welcome to the fireside of your kinsman!

relationships are stronger within the family

Albanian: S'bëhet gjaku ujë
Arabic:
Armenian: արյունը ջուր չի դառնա ‎(aryunə ǰur čʿi daṙna)
Chinese:
Mandarin: 血濃於水 (zh), 血浓于水 (zh) ‎(xùenóngyúshuǐ)
Czech: krev není voda
Danish: blod er tykkere end vand
Finnish: veri on vettä sakeampaa
French: la voix du sang est la plus forte, les liens du sang sont les plus forts
German: Blut ist dicker als Wasser (de)
Greek: το νερό αίμα δεν γίνεται ‎(to neró aíma den gínetai)
Hungarian: a vér nem válik vízzé (hu)
Irish: gach díograis go deireadh, is fearr beagán den ghaol ná mórán den charthanas

Norwegian: blod er tykkere enn vann (no)
Polish: krew nie woda
Portuguese: o sangue é mais grosso que a água
Russian: кровь — не води́ца ‎(krovʹ — ne vodíca) (blood is not water), кровь людска́я — не води́ца ‎(krovʹ ljudskája — ne vodíca) (people's blood is not water)
Scottish Gaelic: is tighe fuil na bùrn
Serbo-Croatian: крв није вода ‎(krv nije voda)
Slovene: kri ni voda (blood is not water)
Spanish: la sangre tira mucho
Swedish: blod är tjockare än vatten
Thai: เลือดข้นกว่าน้ำ ‎(lêuat kôn gwàa nám)
Welsh: gwaed yn dewach na dŵr

Gregory Y. Titelman, Random House Dictionary of Popular Proverbs and Sayings, 1996, ISBN 0-679-44554-4, p. 32.