In a tweet in December 2014, Michael Patrick MacDonald was once again demonstrating his naivety by commenting in relation to the word comhar, which apparently he learned from Cassidy. In reply to someone who gave the real meanings of the Irish word, he said: “Besides whatever dictionary meaning. It’s a long standing ideal of cooperative society.”
In another article on the band the Dropkick Murphys, dated 2012, he also quotes his friend Cassidy about this word:
“Comhar (pron., co’r), n., co-operation; alliance, reciprocity, mutuality; companionship, a cooperative society; cómhar na gcómharsan (pron. co’r na go’ r-arsan), system of reciprocal labor among neighbors, companions, friends, etc.; cómhar na saoithe (pron.co’r na seeh’e), the companionship and society of artists and scholars.”
In fact, Cassidy (and MacDonald) grossly overstated the importance of this word and its centrality to Irish culture. It is mostly used in phrases like ‘ag obair i gcomhar lena chéile’ (working in partnership with each other) or “dhíol mé an comhar leis” (I paid him back for the favour). While it is sometimes used on its own (it is famously the name of an Irish-language magazine) these uses are quite rare. If it really had such a central importance in Irish culture, why has no Irish anthropologist or sociologist (to my knowledge) ever written an essay or an article on it? Where did Cassidy get the idea that it was so important?
The answer is, of course, that Cassidy looked in the dictionaries and found entries describing comhar as mutual work, partnership and cooperation, and the rest came from his imagination. You see, Cassidy claimed to be a socialist (not that his behaviour gave any hint of genuine socialist principles), and so he romanticised Irish by pretending that a kind of peasant communism was built into the very fabric of the language. Of course, there was some degree of collectivism and mutual self-help in Ireland, just as there was in every peasant society but the idea that Irish people lived by the (proto-communist) principle of comhar just as Sicilians followed the code of omertá is just nonsense.
The tweet from Michael Patrick MacDonald is really quite funny. An American who doesn’t speak any Irish is pontificating about the importance in Irish culture of the word comhar, and saying to someone else that it’s quite OK to ignore the dictionary definitions produced by real Irish scholars (Besides whatever dictionary meaning. It’s a long standing ideal of cooperative society). The person who told him about its importance was another American, Daniel Cassidy, who didn’t speak any Irish or know anything at all about the language either! What a joke!
The claim is a pure fake, like everything else derived from the late Daniel Patrick Cassidy and spread like a plague of ignorance by his cronies.
cassidyslangscam 
I am providing a little extra information here, outside the body of the post, to avoid making it too heavy and academic. Dinneen spells this word as cómhar, Foclóir Gaeilge-Béarla (Ó Dónaill) as comhar. Here is Ó Dónaill’s entry for the word:
comhar, m. (gs. -air). Combined work, mutual assistance; co-operation, partnership. Dul i g~ le duine i rud, to combine, co-operate, with s.o. in sth. Rud a dhéanamh i g~ le duine, to do sth. in co-operation, in partnership, with s.o. Ag obair i g~, working together, sharing work. ~ na gcomharsan, neighbourly co-operation. Talamh comhair, land worked conjointly. Tá an bád i g~ acu, they share the boat. Bhí ~ fear, capall, aige, he had men, horses, working for him on a reciprocal basis. An ~ a íoc, a dhíol, a roinnt, le duine, to return a service to s.o., repay s.o. for what he has done for one. Díolfaidh mé an ~ leat! I’ll get my own back on you! Tá an ~ amuigh agat orm, I owe you a service. Ag déanamh comhair le chéile, sharing help, co-operating, with each other. ~ cairdis, friendly co-operation, return. ~ na saoithe, the co-operation, companionship, of learned men. Fear é nach dtéann le ~, he is a person who does not co-operate with others.
The etymology, as given by eDIL, is quite interesting. It originally meant ‘ploughing together, co-tillage, ploughing partnership’, (comh = together, co- + ar = ploughing) hence it acquired the meaning of partnership or union. While the word comharsa (neighbour) looks similar, it has a different origin. It is from comh + ursain (door-frame), so it means people who are next door to each other. Comhar is also (I think) unrelated to the word in phrases like os comhair amach (opposite), where the comhair originally meant ‘in front of’.