Dà is treated as singular. Remember it also causes lenition, dà bhàta, but that is a separate issue.
Originally Indo-European languages had three sets of endings, singular (1), dual (2) and plural (>2). This is obviously a bit fiddlesome and has generally been abandoned but many languages keep tiny wee remnants. Our tiny wee remnant in Gaelic and Irish is that
- We only use the dual after the word dà
- We have forgotten the correct endings and just use the singular. D
I have listened carefully (here) and I am hearing all the phonemes clearly in a pretty standard Gaelic accent. It is very easy to not recognise these phonemes if you are not used to them and they have not been clearly explained, so let's go through them:
- the u is like English put. It is not like words that begin with a u in English that begin with a /j/ (y sound) like union
- The nn is slender (hence written inne). That means it has a /j/ sound attached like in English new (in most dialects). But you may be able to hear this /j/ at both ends of the letter, unlike in the English example
- The a is quite like English back
- The g is like English back. It is not like English bag. It would be pronounced differently if it were a c in Gaelic.
So the best rendition with English spelling would be something like ooynyack. D
Whenever there is a reason for lenition - and it's not restricted to nouns - it is marked/occurs as follows:
- Put an h after b,c,d,f,g,m,p,s,t.
- s does not change, if followed by another letter on the list.
- There is a small sound change for l,n,r but it is not shown in writing.
- No words in Gaelic start with any other consonant (except for a few borrowed words such as heileacoptair, where it is not marked either).
- There is no effect on words that start with a vowel.
- There are certain words that do not lenite d,t and the definite article does funny things to words that begin with an s but these are discussed elsewhere.