[PHP] Replacing exact words

Hi guys, below are simple replacing script a word in to another word, or censorship

[PHP]$word = array(
‘google’,
‘yahoo’
);

$link = array(
‘go*gle’,
‘yah*o’
);

$this->post[‘message’] = str_ireplace($word, $link, $this->post[‘message’]);[/PHP]

the problem its currently also replacing another words like

googler

yahoos

into

go*gler
yah*os

please help how to make it only replacing exact words?
GBU for all that answering