The most common and most likely answer to this crossword clue is the 7 letter word ABYSSES
A
B
Y
S
S
E
S
Buddy explains!

The straight part
We know that "chasms" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case chasms = abysses.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.
What does ABYSSES mean?
ABYSSES noun- Hell; the bottomless pit; primeval chaos; a confined subterranean ocean.
- (frequently figurative) A bottomless or unfathomed depth, gulf, or chasm; hence, any deep, immeasurable; any void space.
- Anything infinite, immeasurable, or profound.
- Moral depravity; vast intellectual or moral depth.
- An impending catastrophic happening.
- The center of an escutcheon.
- The abyssal zone.
- A difference, especially a large difference, between groups.