General:
* La vivienda: This is a very common and neutral synonym.
* El piso: This is another very common synonym, particularly in Spain.
* La casa: This is less precise than "el apartamento," but can be used if you want to refer to a place of residence in general.
More specific:
* La suite: This refers to a luxury apartment, usually with multiple rooms and amenities.
* El estudio: This refers to a small apartment with one main room that serves as living space and bedroom.
* La habitación: This refers to a room in a larger apartment or house.
More informal:
* La morada: This is a poetic and slightly archaic word for "home."
* El hogar: This means "home" and implies a sense of warmth and belonging.
Ultimately, the best synonym for "el apartamento" depends on the specific situation and the meaning you want to convey.