IJzelman- ?

Bearing in mind Venneman's attempt to relate Germanic *i:s- "ice"
with a proposed Basque stem iz- "water" (izurde "water-pig"
ie. "dolphin" etc) and his finding that iz- stem in European place
names all over the place (eg. Ismaning in Bavaria, Isala > IJsel in
Holland) I decide to look it up in Celtic languages.
I found in Welsh:
Isalmaenaidd "Dutch"
Isalmaeneg "Dutch language"
Isalmaenwr "Dutchman"

Odd.

Further :
is "under-, lower"
isel "low, base, depressed"

which could make sense, if we assume a loan into both Basque and
Celtic from language where it meant "shallow, quiet water".

But 'maen' is "stone" in Welsh. On the other hand *man- is one of
Ruhlen's 'world language' stems found all over the place. Therefore
there might have existed a language in which 'Isel-man' meant "a man
from the shallow coast waters". I wonder where Ismaning comes in?

Irish
íseal "low, low-lying, low-voiced, low in water (as a river in
summer), calm (as the sea)"
íseal agus uasal "gentle and simple", ie. "commoner and noble".
So obviously *isel- could also stand for a social class in Irish
Celtic society. This gets interesting.
íslean "a valley, a low place, a descent or incline, a furrow or
groove"

Breton
izel "bas, qui a peu de hauteur"
izelen "lieu bas, vallée, espace entre deux ou plusieurs montagnes"

Basque
beside the supposed *iz- "water" there is
itsaso "sea"
These two cannot be connected within Basque AFIK

Danish:
ising "species of flatfish"
Isefjord, the largest inlet on the island of Sjælland, also known
as 'the sailors' playpen' since it is sheltered from wind and waves.
Two words Vennemann wasn't aware of.

Does anyone know the etymology of Celtic *is(el)- ?

Does a hypothetical **IJzelman make any sense in Dutch (history)?


Torsten