This is the 826th most frequent Slovenian word.
njihovega
The Slovenian word "njihovega" means "their" (possessive, masculine singular genitive form) in English.
Here, 'njihova' refers to someone's possession in a plural form relating to 'their book'.
Njegova knjiga je bila bolj zanimiva kot njihova.
His book was more interesting than theirs.
In this sentence, 'njihovega' functions as an accusative singular masculine conjugation of 'their' corresponding to 'dog'.
Videli smo njihovega psa v parku.
We saw their dog in the park.
Here, 'njihovi' is used as a dative feminine plural adjective referring to 'their future'.