It's an abbreviation of 'sacs-béarla', literally 'saxon language'. Originally 'béarla' meant language in general, but came to mean primarily English. In modern Irish, 'teanga' ('tongue') is typically used for 'language'.
'Béarla' is also sometimes used to mean 'gibberish'.
Etymology corner: the word originated from 'beal-ra', which meant 'something produced by the mouth'. 'Beal' is 'mouth' in Irish.
I don't think they "sort of" brought Old English with them, they just plain did. Haha
I perhaps wasn't precise enough in my definition. What I meant when I said 'language in general' was akin to the contrast between 'langage' and 'langue'. The former refers the the faculty of speech (including voices, gibberish, &c.), while the latter, like 'teanga' refers to specific languages. It could be used to refer to incomprehensible blather in OI, but it was also a component of words like 'bérlamail', which meant 'fluent'.
The English language is a bit odd in that it uses the suffix "-man" for some nationalities but not others ("an Irishman", "an Englishman", "a Frenchman", versus "an Italian", "an American", "a Swede", "a Dane").
The Irish for "Englishman" is Sasanach. A woman from England is also a Sasanach, because, strictly speaking, she also fulfils the dictionary definition of "Englishman".
Right, which is why in the approprate context it can be fine to translate Sasanach as "Englishman" (when you know it refers to a male), but the word can't be said to mean "Englishman" any more than "English woman"
On your second point, not even the fetishized power of dictionaries can make it reasonable to call an English woman an "Englishman"; and I don't think the meaning of the Irish word Sasanach is mediated by any definition of the English word "Englishman".
Yes, the accent, or 'sineadh fada' as it is called, is very important. If left out or put in the wrong place it can convey a completely different meaning. For instance, the word for 'man' is 'fear' and the word for 'grass' is 'féar'. When you're speaking the words sound different so it doesn't cause a problem but when writing, you wouldn't want to tell someone that you cut the man with a scythe:)