Normally I'also expect am "m" word.
Be careful: lexical similarity does not necessarily imply the words are cognates...
In Icelandic milk does not even start with the letter "m", it is "rjómi".
Correct me if I'm wrong, but isn't the word for 'milk' in Icelandic 'mjólk'? I thought 'rjómi' meant 'cream'.
And if you know the ethymology of Icelandic "rjómi", I'd be glad.
It's from the Proto-Germanic '*rauwma-'; although I have no idea what it means. Also, Icelandic 'rjómi' is cognate to (as mentioned) Norwegian 'romme', German 'Rahm', Dutch 'room' and English 'ream'. 'Ream' meaning 'cream', however, has become archaic except in certain dialects of English. ('Ream' meaning a bundle of paper has a different etymology; from Old French 'raime' (modern 'rame') and Arabic 'rizma' meaning 'bundle'...)
The English 'cream' is actually a loanword from Old French 'cresme' (modern 'crème'), a mix of Late Latin 'chrisma' meaning 'ointment' (from Greek 'chrisma', meaning 'unguent') and Late Latin 'cramum' meaning 'cream' (with dubious etymology).
The Icelandic noun 'mjólk' on the other hand, is cognate with (as mentioned) Danish 'mælk', Norwegian 'melk', Swedish 'mjölk', German 'Milch', Dutch 'melk' and of course, English 'milk'.
Both the verb and the noun ('milk' and 'to milk') are from Proto-Indo-European '*melg-' meaning 'stroking, wiping', referring to the hand actions used in milking an animal. The noun is from Proto-Germanic '*meluk-'; the verb from Proto-Germanic '*melkanan' (compare the Old Norse 'mjolk
a' and German/Dutch 'melken').
(Note: The Greek 'amelgein' and Latin 'mulgere' are descended from Proto Indo-European '*melg-' as well
Phew. Too many brackets. Kind of went a bit off, too.
Hope it helped though; and anyone at all is welcome to correct my mistakes.