Before Mass I wait in the same place (6)
I believe the answer is:
ibidem
'in the same place' is the definition.
(synonyms)
'before mass i wait' is the wordplay.
'before' is a charade indicator (letters next to each other).
'mass' becomes 'm' (symbol used in Physics e.g. f=ma).
'wait' becomes 'bide' (I've seen this before).
'i'+'bide'='ibide'
'm' after 'ibide' is 'IBIDEM'.
(Other definitions for ibidem that I've seen before include "In the same book or passage, often abbreviated" , "In reference notes, denotes in the same place" , "Dim I be! (anag)" , "In the same place, used in referencing" , "In the same place (Latin)" .)