, and it has been discussed on this message board before:http://www.behindthename.com/comment/view.php?name=niamh
The poster Deas23242 gave 2 answers, quoted below:
For the Welsh person who is not sure how to pronounce Niamh
. Mh in Irish is NOT like the mh in Welsh which is an unvoiced m as in ym Mhen-y-bont. No it is pronounced like the soft mutated form of m in Welsh which is written f in Welsh & pronounced v. Just as the Welsh word mawr "big" becomes fawr [pronounced /vowr/ after a feminine noun so the Irish word mór "big" is written mhór & pronounced /vo:r/ after a feminine noun. E.G. Welsh: y garreg fawr = Irish: an charraig mhór = the big rock
is pronounced Niaf in Welsh or Niav in English. Some native speakers of Irish pronounce the mh with a slight nasal tinge and this was perhaps the normal pronunciation in earlier times.
-- Deas23242 7/7/2008Niamh
should become Néimhe in the genitive case & should in former times have become Néimh in the dative case. [The dative case is becoming archaic in Irish today [except in cases where it has itself replaced the nominative]]. But though the genitive is much more usual in modern usage, this does not seem to apply to many personal names. An bhfaca tú leabhar Niamh
? would be a more usual usage today than the more correct an bhfaca tú leabhar Néimhe? perhaps.
One explanation for this might be that the name was not in common use as a girl's name in earlier centuries and only existed in the story of Oisín mac Fhinn going to Tír na nÓg with Niamh
Chinn Óir [Bright-(one) of (the) Head of Gold]
Searching all the names in the 1911 census for county Dublin there was one Niamh
& one Neave. These two were both young children which suggests that the name had not been used in the 19th century.
-- Deas23242 7/8/2008