[Regex]::Matches($string, '(?:^|\b)words(?:$|\b)')

Matches only the specific word in the express. In this case words will return, but passwords will not.

PS C:\> $string = 'A passwords should not contain words found in the dictionary.'
>> [Regex]::Matches($string, '(?:^|\b)words(?:$|\b)')



Groups   : {0}
Success  : True
Name     : 0
Captures : {0}
Index    : 31
Length   : 5
Value    : words