This is the 51st most frequent Hebrew word.
אתמול
Yesterday.
The word 'אתמול' denotes the specific time frame of the action, indicating it occurred the day prior to today.
אתמול הלכתי לפארק.
Yesterday, I went to the park.
Here, 'אתמול' sets a temporal context for the descriptive statement, specifying when the cold conditions were experienced.
היה ממש קר אתמול בערב.
It was really cold yesterday evening.
In this sentence, 'אתמול' provides the time indicator for the completed action of meeting someone.