Manager mislaying old earrings (9)
I believe the answer is:
organiser
'manager' is the definition.
(I've seen this before)
'mislaying old earrings' is the wordplay.
'mislaying' is an anagram indicator (I've seen 'mislaid' mean this).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'o'+'earrings'='oearrings'
'oearrings' with letters rearranged gives 'ORGANISER'.
(Other definitions for organiser that I've seen before include "Co-ordinator" , "One managing" , "Rosie rang the person in charge of the arrangements" , "One making arrangements" , "impresario" .)