Letter from Greece slipped into our house (3)
I believe the answer is:
rho
'letter from greece' is the definition.
(letter from the Greek alphabet)
'into our house' is the wordplay.
'into' says the answer is hidden in the clue.
'RHO' is hidden in the letters of 'our house'.
'slipped' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for rho that I've seen before include "Gr. letter written as P" , "letter to Athens" , "Something like 25 [ETA]" , "Greek character" , "Sophocles character" .)