Out to lunch, say (6)
(Other definitions for eating that I've seen before include "Consuming food" , "Having supper?" , "Ingestion" , "Out to dinner?" , "at breakfast?" .)
'out to lunch say' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for not in that I've seen before include "ie Out" , "Out or away, house empty" .)