Scottish Gaelic spelling variant of Janet [q.v.].
A correspondent [IHM] has reported this spelling in a birth record of 1838 in a family bible, written at a period when the family were Gaelic speakers. In the census the child was recorded as Janet and known to the family as Jessie (recorded on a memorial stone). It is felt that the spelling, Jonnat, is a phonetic spelling of the Gaelic pronunciation.