This is the 3720th most frequent Catalan word.
acostant
"Acostant" means "approaching" or "bringing closer" in English.
Here 'acostant-nos' is a reflexive verb form indicating 'getting closer'.
Estàvem acostant-nos al cim de la muntanya.
We were approaching the mountain's summit.
In this case, 'acostant-se' is showing progression towards a conclusion.
Està acostant-se al final del llibre.
He is approaching the end of the book.
Here 'acostant' implies actively moving an object closer.