Getting rows in left table only if not present in the right table
Here is an example : 

SELECT 
    a.col1
    , a.col2
    , a.col3 
FROM 
   table1 a
   LEFT JOIN table2 b 
       ON 
           (a.pkcol = b.pkcol)
WHERE 
   b.pkcol IS NULL


So in your case, it will most likely be : 

SELECT 
    n.seqid
    ,n.wordindex
    ,n.label
    ,n.arg1
    ,n.arg2
    ,n.sublabel 
FROM 
    newparsed n
        LEFT JOIN   advlabel a 
            ON 
                ((a.`seqid` = n.`seqid`) 
            AND 
                (a.`wordindex` = n.`wordindex`))
WHERE 
   a.`seqid` IS NULL


You just have to use LEFT JOIN and select any field (I suggest a primary key) in the right table that is NULL