Θα κάθομαι στο σαλόνι μέχρι να έρθεις.

I will be sitting in the living room until you come.

Breakdown of Θα κάθομαι στο σαλόνι μέχρι να έρθεις.

• έρχομαι: to come
• θα: will
• σε: in
• το σαλόνι: the living room

Questions & Answers about Θα κάθομαι στο σαλόνι μέχρι να έρθεις.

What exactly does θα κάθομαι mean here, and why is it not just θα κάτσω or θα καθίσω?

Θα κάθομαι is the future continuous / progressive form of κάθομαι.

• Θα κάθομαι στο σαλόνι μέχρι να έρθεις.
  = I’ll be sitting / I’ll be (staying) in the living room until you come.

It presents the action as ongoing over a period of time up to the moment you arrive. The focus is on the state or duration.

Contrast:

• Θα κάτσω / Θα καθίσω στο σαλόνι.
  = I’ll sit (down) in the living room.
  This is more like a single act of sitting down, not so much the whole period of waiting.

In your sentence, the speaker wants to say “I will be there (sitting, staying) during that whole time until you arrive”, so Greek prefers θα κάθομαι (continuous aspect).

Why is the verb κάθομαι in the “-ομαι” form? Is it reflexive or passive?

Κάθομαι is a verb that only appears in the middle/passive endings (-ομαι) in Modern Greek, but with active meaning:

• κάθομαι = I sit / I’m sitting / I stay seated / I’m staying (somewhere)

Historically, Greek had an active form (κάθω), but in modern usage you only meet κάθομαι, so you can just treat it as the normal dictionary form meaning “to sit / to be sitting”.

It is not reflexive in the English sense (“I sit myself”), and it’s not passive (“I am sat by someone”). It’s just the regular way to say “I sit / I’m sitting” in Greek.