This is a container clue - one word or set of letters goes inside another word to form the answer.
Take either the first or last letter of the word at position 9 in the grid, then put it inside a word meaning 'bank' or 'slope'. The result is a 7-letter word.
Answer: CHAMBER | Take H (first or last letter of HEATH, which is at 9 across/down) and put it inside CAMBER (meaning to bank or slope) to get CHAMBER (vault).