Old Irish castle emptied out for meeting with the dead (6)
I believe the answer is:
seance
'old irish' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'castle emptied out for meeting with the dead' is the wordplay.
'emptied' says to hollow out the word (remove centre letters).
'out for' becomes 'n' (I can't justify this - if you can you should give a lot more credence to this answer).
'meeting' says to put letters next to each other.
'with' means one lot of letters go next to another.
'the dead' becomes 'sea'.
'castle' with its middle removed is 'ce'.
'ce' put after 'n' is 'nce'.
'nce' after 'sea' is 'SEANCE'.
Can you help me to learn more?
(Other definitions for seance that I've seen before include "Session for spiritualists" , "Spiritualist meeting, all hold hands" , "spiritual guidance" , "Spirit meeting" , "Dead rousing session" .)