This is the 3rd most frequent Swedish word.
som
The Swedish word "som" means "as," "like," "who," "which," or "that," depending on context.
Here, "som" is used as a comparison word, showing equality between two subjects, "hon" (she) and "sin syster" (her sister).
Hon är lika snäll som sin syster.
She is as kind as her sister.
In this example, "som" functions as a preposition meaning "as," describing a role or capacity in which the subject, "hon" (she), acts.
Som chef måste hon fatta många beslut.
As a manager, she has to make many decisions.
In this sentence, the word "som" acts as a relative pronoun and introduces a subordinate clause, giving more information about the noun "bok" (book).