The most common and most likely answer to this crossword clue is the 7 plus 3 plus 3 plus 4 letter word ARSENIC AND OLD LACE
I've seen this crossword clue in Independent
A
R
S
E
N
I
C
A
N
D
O
L
D
L
A
C
E
Buddy explains!
The straight part
We know that "it starred Cary Grant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case it starred cary grant = arsenic and old lace.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.