I found this in Dinneen's dictionary:
Quote:
nach, conj., (eclipses in modern Irish), that not; ó nach (colloq. uair nach), since not; go nach (go dtí nach), until not; assertive verb is omitted after nach (which does not then eclipse); is fíor nach díon dóibh crainn, it is true that trees afford them no shelter; before pf. tense it combines with ro becoming nachar, which see; after negatives, expressed or implied, ná go is used in M. for nach; the eclipsis caused by nach is quite modern; beag nach, beagnach, little but, almost, nearly.
Since you brought it up, do you know of any comprehensive list/study of Irish idioms that require the negative such as this and others like
ní h-ar aon chuma amháin as Ó Laoghaire provided?