This is the 125th most frequent Icelandic word.
sínu
The Icelandic word "sínu" is the dative singular form of "sinn," meaning "one's own" or "his/her/its own."
Here, 'sínu' is used to denote possession in relation to the subject ('Hann'), indicating that the child belongs to him.
Hann færði sínu barni gjöf.
He gave his child a gift.
In this sentence, 'sínu' refers back to 'Hún' to indicate that the people are related to her in some way, showing a possessive relationship.
Hún bað um að hafa tíma með sínu fólki.
She asked to have time with her people.
Here, 'sínum' (the masculine plural dative form) refers to another group not including the subject, contrasting whose terms are being considered.