‘caser’ could be a form of ‘kaiser’ or ‘ceasar’ and ‘-dom’ is the suffix as in ‘wisdom’ and ‘freedom’. The same suffix exists in Dutch, where it had originally the same meaning as ‘doem’ (English ‘doom’), meaning ‘honour’ and ‘place (in society)’. Earlier it meant ‘judgement’. Together: emperor’s judgement.
Old English Wordhord 
‘caser’ could be a form of ‘kaiser’ or ‘ceasar’ and ‘-dom’ is the suffix as in ‘wisdom’ and ‘freedom’. The same suffix exists in Dutch, where it had originally the same meaning as ‘doem’ (English ‘doom’), meaning ‘honour’ and ‘place (in society)’. Earlier it meant ‘judgement’. Together: emperor’s judgement.
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Yes, Old English dōm means many different things like that, judgment, law, power, etc.: http://bosworth.ff.cuni.cz/007799.
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