Adam Clarke on Mark 9:24

Lord, I believe - The word Lord is omitted by ABCDL, both the Syriac, both the Arabic later Persic, Ethiopic, Gothic, and three copies of the Itala. Griesbach leaves it out. The omission, I think, is proper, because it is evident the man did not know our Lord, and therefore could not be expected to accost him with a title expressive of that authority which he doubted whether he possessed, unless we grant that he used the word κυριε after the Roman custom, for Sir.

Help thou mine unbelief - That is, assist me against it. Give me a power to believe.