This is the 102nd most frequent Greek word.
διάστημα
"Διάστημα" in English means "space" (as in outer space) or "interval" (as in time or distance).
In this sentence, 'διάστημα' refers to outer space.
Το διάστημα είναι γεμάτο αστέρια.
Space is full of stars.
Here, 'διάστημα' refers to a span of time being discussed.
Έχει μεγάλο διάστημα που δεν τον έχω δει.
It has been a long time since I last saw him.
In this usage, 'διάστημα' means a time period or interval.