PS

*mVr(V)r-at- - gall, gall bladder (SED I No. 188; Kogan 2011: 219)

Most Sem. forms with a reduplicated second radical may be derived after various deverbal paterns from *mrr ‘to be bitter’. However, the fact that besides nominal forms meaning ‘bile, gall, gall-bladder’, there are also terms throughout Sem. meaning only ‘gall-bladder’, and even ‘bladder’ (in Gur). and ‘stomach’ (in Soq.), makes one doubt that this anatomical term derived from the verb ‘to be bitter’; a contamination with this verb (especially in case of Arm. and Hbr. pB. ‘poison’) is very likely.

Akkadian
martu - gall, gall bladder (CAD M₁ 297, AHw. 614)
pl. marrātu
Hebrew
mərōrā, mərērā - gall-bladder (HALOT 639)
Jewish Babylonian Aramaic
mərirtā - gall (Jastrow 843)
Syriac
mrārāta - gall (LSyr. 400, SL 839)
Syriac
mertā - gall, bile (LSyr. 400, SL 839)
Mandaic
mirta - gall, bile, venom (MD 270)
Arabic
mirrat- - fiel, bile (gall, bile) (BK 2 1084, Lane 2701)
Tigre
märänät - gall (WTS 114)

The difficulties are as follows: 1) the gemination of r­ may not be marked; ­2) n­ is to be explained either as a suffix or as a result of dissimilation from *mVrār-­at-­. In any case, the meaning is a decisive argument for relating the Tgr. form to the present root. 

Argobba
märara - bile (LArg. 213)
Harari
mərār - bile (EDH 111)
Mehri
mərrāt - gall, gall-bladder (ML 268)
Jibbali
mεrrɔ́t - gall-bladder (JL 173)
Harsusi
merrét - bile, gall (HL 89)