lo ‧ cum /ˈləʊkəm $ ˈloʊ-/ BrE AmE noun [countable] British English
[ Date: 1900-2000 ; Origin: locum tenens 'someone who takes someone else's place for a time' C17- 21), from Latin , 'holding the place' ]
a doctor or priest who does another doctor’s or priest’s work while they are on holiday, ill etc