מסתּמא
מִסְּתָמָא
מסתּם
'probably'

ETYMOLOGY

a for old kamatz -- a relic of the pre-Ashkenazic pronunciation {מאַקס ווײַנרײַך, געשיכטע פֿון דער ייִדישער שפּראַך, 2: 12}

LINK: http://www.dovidkatz.net/WebAtlas/23_Probably.htm
'probably'
LITVISH: An Atlas of Northeastern Yiddish by Dovid Katz

WESTERN

Oyberland (West Transcarpathian)

mɩstóːmə {WTCP, Vác, 47197}

mɩstóˑmə {WTCP, Berettyó-Újfalu, 47212}

CENTRAL

Unterland (East Transcarpathian)

mistám ~ mistúmə {ETCP, Sîg Felső Szek, 47223}

mɩstam {ETCP, Mukachevo, 48226}

mistám {ETCP, Nyzhnya Apsha, 48233}

mɩstúm {POLAND, Wolbrom, 50196}

mistumɩ {POLAND, Warsaw, 52211}

HASIDIC

AMERICA

<מסתם> ~ <מסתמא>
mɩstumə

NORTHEASTERN

misstom 'wahrscheinlich' {Grajewo, Olsvanger 1931}

Lithuania

mʲistome {LITHUANIA, Vilnius, 54257}

SOUTHEASTERN

mistɔ́m {ROMANIA, Brăila, 45273}