Spanish Grammar/Common Masculine Noun Endings
As a general rule, most masculine nouns end in -o. But there are many other noun endings. There are some general rules you can memorize to help you recognize masculne nouns even if they don't end in -o.
Many masculine nouns end in -aje. These nouns are almost never feminine.
Many nouns ending in -ma, -pa, or -ta are also masculine.
LONERS nouns: nouns ending in -l, -o, -n, -e, -r, or -s are usually masculine.
Most of the time, a noun that ends in an accented vowel is masculine as well.
There are always exceptions, but remember these generalizations.