מאַרך
'marrow; brain'

ETYMOLOGY

Beider writes that the soource of the final [x] is obscure, because most German dialects have final [k], like Standard German.

{Beider 2015: 95.}
But variants with [x] are evident in MHG and OHG - so [x] is probably a retention.
MHG marc, march; from OHG marg, marag, march.
{DW¹ 12: 1628. Lexer 1: 2041}
ON margr; OE mearg, mearh; English marrow; OS marg; Middle Low German march; OHG marg; from PGmc ✱mazg-a-; from PIE ✱mosghó-; cf. Avestan mazga- 'marrow, brain'.

WESTERN

Alsace (France)

ˈmarɩg {ALSACE, 47075 Mulhouse, 015-060}

Oyberland (West Transcarpathian)

márɔx {אויך אין געהירן} {WTCP, Dunajská Streda, 47179}
- márəxbaˑ מאַרכביין

marəx {WTCP, Vác, 47197}
- marəxbajn מאַרכביין

márəx {WTCP, Berettyó-Újfalu, 47212}

CENTRAL

Unterland (East Transcarpathian)

marɜx m. 'Mark' {ETCP, Beranek 1941}

máræx {ETCP, Sîg Felső Szek, 47223}

marəx {ETCP, near Sighet, 47228}

dər márəx {ETCP, Mukachevo, 48226}

marˑx {ETCP, Nyzhnya Apsha, 48233}

maʀəx {פֿון ביין} {POLAND, Wolbrom, 50196}

a marx '(rear of head)' {POLAND, Warsaw, 52211}

NORTHEASTERN

marx {BELARUS, Gomel, 52314}

Lithuania

marx {LITHUANIA, Kaunas, 54239}

SOUTHEASTERN

marəx {אין די ביינער} {ROMANIA, Brăila, 45273}