In Greek there are three grammatical gender: feminine, masculine and neuter.
Commonly the grammatical gender can be recognized by taking a look at the substantive’s ending.
Nevertheless the noun's gender should be memorised together with the noun.

Masculine nouns

In Greek masculine nouns commonly have -ος, -ας, -ης endings.

💡 Examples:
ο φίλος – the friend
ο γιατρός – the doctor
ο χειμώνας – the winter
ο ήρωας – the hero
ο καθηγητής – the teacher/professor
ο μαθητής – the student

Feminine nouns

In Greek feminine nouns commonly have a -α or -η ending.

💡 Examples:
η φίλη – the (female) friend
η οθόνη – the screen
η καθηγήτρια – the (female) teacher
η γάτα – the cat

Neuter nouns

The Greek neuter nouns usually end in -ο, -ι, -μα.

💡 Examples:
το κινητό – the mobile phone
το δέντρο – the tree
το σπίτι – the house
το ποτήρι – the glass
το μάθημα – the lesson
το δέμα – the package