This is the 258th most frequent Polish word.
jednego
"Jednego" means "one" or "of one" (genitive case, masculine singular) in English.
The word 'jednego' here is used to indicate 'one out of a group', referring to a specific friend out of a broader group of friends.
Zaprosiłem jednego z moich przyjaciół na kolację.
I invited one of my friends to dinner.
The word 'jednego' is used in its masculine singular genitive form to indicate the passage of „one year”.
Pamiętam to zdarzenie, jakby wydarzyło się wczoraj, choć minęło już jednego roku.
I remember this event as if it happened yesterday, although a year has already passed.
The word 'jednego' is used in congruence with a possessive relationship to express a part of one, in this case, modifying 'company' as one of the best.