Graiméar na Gaedhilge (1906)
I don't remember seeing a link to this before, but I just came across the 1906 edition of the Christian Brothers Graiméar na Gaedhilge on Wikisource.
The book is written in English, and uses pre-reform spelling (like Gaedhilge) for the examples in Irish, so you might want to be careful about following it's advice in all situations, but the explanations are clearly written, and may be helpful.
Note that Graiméar Gaeilge na mBráithre Críostaí (I have a copy published in 1999) is in Irish - the basic order of tyopics is similar but I haven't really compared them to see how closely related they are.
Ní raibh a fhois agam riamh go bhfuil comhráite Gaeilge ar siúl sa fóram ar an suíomh seo, tá sé sin go hiontach! Déanfaidh mé iarracht a bheith páirteach chun cleachtadh Gaeilge a dhéanamh.
…not to mention some 18th-century dictionaries of Irish and Saics-Béarla, with many, many words that have ceased to be.