There’s been a few discussions on the sub around the topic, but zoning specifically on the Irish famine here’s a few answer:
The Irish Potato Famine (1845-1852), while often viewed as a tragedy, largely escapes being labelled as a genocide by the academic community. In contrast to this, the Holodomor/Soviet Famine (1932-1933) is actively labelled as a genocide by 16 countries. What are the causes behind this difference? with answer by u/eddie_fitzgerald
Was the Irish famine of 1845-49 due to English government policies or were other factors in play? As a follow up, can it be called a genocide? with answers by u/Instantcoffees and u/Balnibarbian
I often hear people say that the Irish Potato Famine was more a genocide than a true famine. How accurate is this claim? with answers by u/Cenodoxus and u/Instantcoffees
Did Britain actually cause The Great Famine/Hunger in Ireland? with answer by myself
Whether one should approach the Holodomor with a lens of genocide is still an unresolved question in academia. There are valid arguments for and against. Here are some threads on the matter:
hamiltonkg's first post has been eaten by reddit for containing dot ru links; it is reproduced, links sanitised, here.
For posts on the Bengal Famine, see next post.
I'll in part some thoughts on the answer due to recent debates in our own history department here.
Part of the answer comes from politics and the other comes from semantics. Firstly, many historians are just like any other people - we are motivated by politics, informed by scholars who were motivated by politics, and driven by politics to create and write history texts that are topically relevant in a given time. Many American scholars have been deeply critical of the Soviet Union in a variety of aspects for a few different reasons. One is straight Cold War patriotism of America=Good, Soviet=Bad mentalities. Secondly, (some) Marxists scholars have been critical of the Soviet Union as a potential example of socialism done poorly. Thirdly, many scholars are simply critical of states and state actions and so they'll study and explain the failings in and around Holodomor.
Rather simply put here, if you're anti-Soviet/anti-Stalin, you have good motivation to use the word "genocide" in relation to Holodomor, as opposed to some sort colossal governance blunder.
Yet, in our department, the biggest issue comes down to intent. Many scholars define genocide somewhere along the lines of an intent to exterminate a population. When looking at the Irish Famine in particular, there's numerous primary sources of parliamentary conversations and plans on how to improve Ireland's infrastructure, society, and resolve the potato famine itself. Not that the English here wanted to preserve Ireland - they definitely wanted to drastically change it, but the claim they wanted to kill the Irish is more difficult to assert.
With retrospect, we can see bigotry and racism at play with how deeply the British loathed the Irish, overlooked their needs, and made numerous blunders of governance. But, proving that the British government intended to eradicate and kill off hundreds of thousands ( a million) of Irish people is much harder to prove. So if a given scholar is determined that genocide can only exist when intent is present, then they can argue all the horribleness of the Potato Famine, but not give it the genocide label. (This happened here with our British scholar, much to my own personal frustration which is neither here nor there.) Finding that smoking gun that proves intent is much, much harder.
Which brings us back to Holodomor. Did Stalin intend on starving out Ukrainians to prevent an independence movement? That's hard to prove, but some accept it as a likely given due to other harsh policies and a general interpretation of various socialist dictators (whether actual dictators or perceived) as so widespread, the genocide couldn't logically be accidental (in that logic).
So the answer really lies within semantics. How does one define Genocide, what evidence do they acknowledge (and/or know of)? If we begin to relax that hinge-upon-intent definition, a lot of government actions will fall under genocide. For some scholars, this is problematic as it severely downplays those then-intentional genocides like the Holocaust and others.
It all boils down to semantics and intent. A genocide is described as the murder of a large number of people from a particular nation or ethnic group, with the aim of destroying that nation or group, did the Soviets higher ups openly stated in official communications or private documents that they intended to exterminate Ukraine's population or at least part of it? They certainly did say it was imperative for the central government to strike down Ukrainian opposition movements but going from that to a genocide seems kind of stretch to some, with all due respect to the victims in this prospective the Holodomor appears more like an unwanted consequence of a disastrous agricultural policy which met little to no corrections from the central government once in Moscow they realised their actions were leading many to die.
The same logic must apply to the Irish and Bengali case: do we have some sorts of documents attesting a specific intention from the British to kill in mass huge part of Ireland and Bengal's respective population? Not really, we do have documents describing both the Irish and Bengali people as a threat which needed to be dealt with, and for the Irish one could make the case a cultural genocide was intentionally carried by the Brits during many centuries but regarding the famines once again the word genocide may appear to be kind of a stretch to some scholars, like in Ukraine's case it seems the mass deaths were a result of bad policies which met little to no correction during their tragic evolution, whether that constitutes a genocide or not is influenced by ones definition on the matter of what a genocide actually is.
One must also note that our understanding of the word genocide is highly influenced by Jewish holocaust which involved the direct imprisonment and killing of the Jewish population by the Nazis, famines in our general prospective are because of that viewed as an indirect genocidal tool which for some scholars do not constitute a genocide per say.
EDIT: bottom line is if you consider the Holodomor to be a genocide (and looking from different prospectives you could rightfully do so) then logic dictates you should consider the Irish and Bengali famines as genocidal acts too, if you don't consider Holodomor a genocide then consequently the Irish and the Bengali case should also escape that definition.