This is the 6735th most frequent Russian word.
si
The Russian word "si" does not have meaning in standard Russian; it might be a non-Russian term or a typo.
The word 'сиамских' is part of the phrase 'сиамских кошек,' meaning 'Siamese cats,' describing a specific type of cat.
Этот человек сказал, что видел сиамских кошек.
This person said that he saw Siamese cats.
The word 'Си' here refers to 'SI,' the abbreviation for the International System of Units.
Си есть международный стандарт единиц.
The SI is the International System of Units.
The word 'если' means 'if' in English, introducing a conditional clause.