See the current Perl documentation for Search::Dict.
Here is our local, out-dated (pre-5.6) version:
Search::Dict, look - search for key in dictionary file
use Search::Dict; look *FILEHANDLE, $key, $dict, $fold;
Sets file position in FILEHANDLE to be first line greater than or equal (stringwise) to $key. Returns the new file position, or -1 if an error occurs.
The flags specify dictionary order and case folding:
If $dict is true, search by dictionary order (ignore anything but word characters and whitespace).
If $fold is true, ignore case.