Ceremonial trial rearranged about the middle of January (6)
I believe the answer is:
ritual
'ceremonial' is the definition.
(I've seen this before)
'trial rearranged about the middle of january' is the wordplay.
'rearranged' indicates an anagram.
'about' indicates putting letters inside.
'the middle of' says to take the centre.
The middle of 'january' is 'u'.
'trial' with letters rearranged gives 'rital'.
'rital' placed around 'u' is 'RITUAL'.
(Other definitions for ritual that I've seen before include "Regular stereotyped action" , "Actions performed as in a religious ceremony" , "Code of ceremonies" , "Ceremony or protocol" , "Customary observance or practice" .)