higlighting problem: shouldn't highlight one letter at a time

What's wrong with this:

for($m=0; $m <  count($bigWords); $m++){
		$strText = preg_replace("/(".$keyword[$m].")/i", "<span class=\"\" id=\"\" style=\"color:".$COLORS[$m]."; 							font-weight:bold;\">$1</span>", $strText);
		echo "<br />";
		echo $strText;
	}

PHP:

It's highlighting one letter at a time:

<span class="" id="" style="color:red; font-weight:bold;"></span>
t<span class="" id="" style="color:red; font-weight:bold;"></span>
h<span class="" id="" style="color:red; font-weight:bold;"></span>
e<span class="" id="" style="color:red; font-weight:bold;"></span>
 <span class="" id="" style="color:red; font-weight:bold;"></span>
w<span class="" id="" style="color:red; font-weight:bold;"></span>
h<span class="" id="" style="color:red; font-weight:bold;"></span>
o<span class="" id="" style="color:red; font-weight:bold;"></span>

 <span class="" id="" style="color:red; font-weight:bold;"></span>
a<span class="" id="" style="color:red; font-weight:bold;"></span>
n<span class="" id="" style="color:red; font-weight:bold;"></span>
d<span class="" id="" style="color:red; font-weight:bold;"></span>
 <span class="" id="" style="color:red; font-weight:bold;"></span>
b<span class="" id="" style="color:red; font-weight:bold;"></span>
u<span class="" id="" style="color:red; font-weight:bold;"></span>

Code (markup):

 

What is the $keyword variable..? It seems like it's a string and not an array so doing $keyword[$m] would do one letter at a time from the string. Since you're doing it from count($bigWords), shouldn't you be using $bigWords[$m] in the preg_replace?

 

I realized when I pasted that section the $keyword wasn't mentioned before. And echo $strtext should be placed outside the for loop.