Steep charge to secure home? Mother’s on to it (8)
I believe the answer is:
marinate
'steep' is the definition.
(marinating is a kind of steeping)
'charge to secure home? mother's on to it' is the wordplay.
'charge' becomes 'rate' (rate is a kind of charge).
'to secure' means one lot of letters goes inside another.
'home?' becomes 'in' ('he's home' can mean 'he's in').
'mother' becomes 'ma' (Ma is another word for mother or mum).
'on to it' is a charade indicator (letters next to each other) (in a down clue, some letters go above others).
'rate' placed around 'in' is 'rinate'.
'rinate' after 'ma' is 'MARINATE'.
(Other definitions for marinate that I've seen before include "steep in liquor" , "Steep before cooking" , "Soak meat, fish etc" , "Soak meat in seasoned liquid before cooking" , "Rain team (anag.)" .)