I've just moved to Switzerland and my dictionaries haven't caught up with me yet, so if you could list some more of the examples from Ó Dónaill it would be helpful.
quote:Does the fact that in these cases 'idir' refers to two words separated by 'agus' have anything to do with it?
Sorry, I don't understand what you're getting at here. In
all the examples above, "idir" has two objects, separated by "agus" or by "is" (="agus").
"Idir shúgradh is dáiríre" doesn't mean somewhere midway between joking and serious - it means
both joking and serious at the same time. Ditto for "idir gháire is ghol." So lenition makes sense. No real idea why "dáiríre" isn't lenited too, but here are a couple guesses:
(1) Overzealous application of "DeNTaLS." (Idir shúgradh is d(h)áiríre atá mé!)
(2) When a preposition - any preposition - has a compound object, initial mutations do tend to be dropped from the second noun.
e.g. "le sean agus óg" (rather than "hóg")
I imagine that stock phrases like those you've mentioned would have a stronger chance of escaping this fate - certainly "idir bhuachaillí is cailíní" sounds a whole lot less weird (to me anyway) than "idir fhir agus mná".