Some invocation in the ordinal (5)
I believe the answer is:
ninth
'ordinal' is the definition.
(similar in meaning)
'some invocation in the' is the wordplay.
'some' says the answer is hidden in the clue (some parts of the word are used).
'NINTH' is hidden in the letters of 'invocation in the'.
(Other definitions for ninth that I've seen before include "Next after eight" , "Ordinal number" , "Beethoven's "Choral", for example" , "Beethoven's last?" , "interval" .)