This is the 724th most frequent Finnish word.
isä
Father.
'Isäni' is a possessive form meaning 'my father', where 'isä' roots the word to mean 'father'.
Isäni on töissä kaupungissa.
My father works in the city.
'Isä' is used as a subject noun delineating 'father' in a general descriptive sentence.
Isä rakastaa lapsiaan.
Father loves his children.
'Isä' is used as a direct object noun, identifying the relationship of 'father'.