Holly possibly sending up cross priest (4)
I believe the answer is:
ilex
'holly' is the definition.
(I've seen this before)
'sending up cross priest' is the wordplay.
'sending up' is a reversal indicator (in a down clue, letters go up).
'cross' becomes 'x' (X is cross-shaped).
'priest' becomes 'eli' (biblical figure).
'x'+'eli'='xeli'
'xeli' back-to-front is 'ILEX'.
'possibly' acts as a link.
(Other definitions for ilex that I've seen before include "Genus of trees that includes hollies" , "'Tree group, includes holly (4)'" , "The holly family of trees" , "Holly, perhaps" , "Holly, classically" .)