As you already know, ainmearan (nouns) in Gaelic can be either boireann (feminine) no fireann (masculine) and this will affect how the noun changes in na tuislean (the cases).
Even though the best way to learn the gnè (gender) of a noun is to learn it with a buadhair (adjective) for example sgeulachd mhath, oidhche mhath, feasgar math, taigh math (further examples below), there are other ways.
oidhche mhath
good night
Fraingis bhrèagha
beautiful French
aimsir bhruthainneach
sultry weather
doras geal
white door
naidheachd mhath
good news
mionaid bheag
a little minute(!)
sgìre mhòr
a big district/area/parish
eilean dubh
dark island
Bliadhna Mhath Ùr
Happy New Year
Gàidhlig bhrèagha
beautiful Gaelic
bàta beag dearg
a little red boat
bò Ghàidhealach
a Highland cow
Some words: cainnt, tìde, aimsir are boireann (feminine), but the litreachadh (spelling) can also give us an idea.
rìoghachd (f)
kingdom
A’ Ghàidhealtachd (f)
The Highlands
iarlachd (f)
earldom
A’ Ghalltachd (f)
The Lowlands
poblachd (f)
republic
siorrachd (f)
shire, county
We have seen a few nouns ending –chd, (pronounced ‘chk’). These are always feminine when they have more than one syllable. There are a few short nouns ending in –chd which are masculine. These nouns don’t change their endings in different cases.
naidheachd (f)
news
siorrachd (f)
shire/county
sgeulachd (f)
story
dreuchd (f)
job/career
iarlachd (f)
earldom
rìoghachd (f)
kingdom
beachd (m)
opinion, view, idea
achd (m)
act, statute
dreachd (m)
draft