This is the 3386th most frequent Russian word.
посла
"Посла" is the genitive or accusative singular form of "посол," which means "ambassador" in English.
Here, 'посла' is used in the genitive case of the noun 'посол' (ambassador), indicating possession, as in 'the letter of the ambassador' or related to the ambassador.
Я отправил письмо посла.
I sent the letter to the ambassador.
The form 'послом' demonstrates the instrumental case of 'посол', used here to denote 'with the ambassador' as the noun serves as an instrument or accompaniment in the action.
Вчера мы встретились с послом.
Yesterday we met with the ambassador.
The word 'посла' appears in the genitive case, showing a relationship or connection (tasks belonging to the ambassador).