Lenition in Scottish Gaelic
How do I know which nouns are masculine or feminine
I got this from Gaelic With Jason. He says there are a lot of exceptions and nothing beats looking the noun up in a dictionary and finding out for sure, but if you want to guess there are some hints.
Masculine: male things (like tarbh), and word endings -ach, -adh, -an, -as, -ir, -iche, and last vowel broad. Video here https://www.youtube.com/watch?v=54bgc2nibF8
Feminine: female things (like bò), and word endings -ag, -achd, -id, and last vowel slender. Video here https://www.youtube.com/watch?v=yqOxGKdVD9s
Then of course boireannach is masculine, so who can say?
This is a common problem when learning any language with gender distinctions. When learning French and German this is very difficult, as articles in front of a noun vary depending on the gender of a word.
German: Der Mann, die Frau, das Kind (yes German grammar has 3 genders!). French: le garçon, la famme.
While people often try to find shortcuts to figure out which is which, there is unfortunately never a rule that holds up across the entire language. The only way to learn is through exposure and repetition.
Don't worry too much about getting the gender of the word wrong when you start off (there's probably plenty of other things you do that also show you are a beginner). Just keep practicing and trying until you get it right. Explicitly studying for each individual word whether its masculine or feminine is a waste of brain space if you ask me. Just take note of the mistakes you make and eventually you'll subconsciously learn which words are masculine and which are feminine. It works for babies and children so it should work for us as well, it'll probably only take a bit longer.
There isn't an easy way, but if you don't mind a little reading, Akerbeltz has a few pages in Beagan Gràmair that might help.
One is called "How to gender a noun"
The other two are separate pages for Masculine and Feminine Nouns:
There is also a page on lenition (for your subject line) here