Lead-in to "cotta" or "firma" (5)
I believe the answer is:
terra
'lead-in to cotta or firma' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for terra that I've seen before include "Land (Latin)" , "Centre" , "Legally land" , "Latin word for earth" , "-- Firma; -- incognita" .)