Hello! I am interested in words that, over time, have lost the sound of some of the consonants that make up the word.

Is Comharsa (Neighbor) an example?

What about Comhaireamh (counting).

How about Tabhair (give)

What sounds have been lost? What are some other words like this?

Thank you for your time.

I don't know if I would classify the examples that you gave as 'lost consonant sounds'. Sure, in most dialects, the consonant itself has been largely lost and very different from what would be the original phoneme (e.g. comharsa --> /kõ:rsə/ in Munster), but even with that a new phonetical realisation has occured, that being the lengthening of the /o/ vowel (which in some cases has become /u: ~ ũ:/). In some dialects in Ulster, the original phoneme (in the examples you provided) has been preserved to an even higher level (i.e. /kowərsə/), but I believe that the modern dialects in the north that preserve this are now few as a result of the imperialistic and oversimplified Caighdeán. There are some phonemes, however, that have been virtually erased throughout all dialects as distinct phonemes, such as the fortis or strong /r/ phoneme (i.e. /R/ or /ʀ/ as many Irish linguists right it), which is essentially a trill as opposed to the normal flap. No dialect that I know of has this as a distinct phoneme that would occur in the environments where it would have normally be found (i.e. at the beginning of (most) words in unlenited contexts, and before dental consonants). The strong/fortis slender /r/ (/R´/ or /ʀ´/) has for sure disappeared in every dialect. But I don't think that this is the kind of 'phantom consonant' that maybe you were asking about?

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I'm an intermediate speaker of the Corca Dhuibhne dialect of Irish and also have knowledge on the old spelling
Soir gaċ síar, fé ḋeireaḋ thíar