This is the 53rd most frequent Hebrew word.
אחת
"One" (feminine).
Here, 'אחת' means 'one' referring specifically to a singular but part of a greater set.
זו הייתה אחת החוויות המיוחדות ביותר שהיו לי.
This was one of the most special experiences I've ever had.
In this sentence, 'אחת' is used metaphorically to indicate an exemplary member within the group.
אחותי הקטנה היא אחת הילדות הכי חכמות בגן.
My little sister is one of the smartest kids in kindergarten.
'אחת' here emphasizes singularity, particularly 'one', referring to the female recipient.