The most common and most likely answer to this crossword clue is the 9 letter word NOSTALGIA
N
O
S
T
A
L
G
I
A
More clues leading to the result NOSTALGIA
- Left in Santiago, desperately yearning for the past
- Sentimental feeling again lost at sea
- Lost again at sea, looking back over one's course?
- Longing, looking back again, lots fancy
- Longing for battle, lost again
- Longing to be lost again at sea
- Giant also upset in homesickness
- Lost again at sea, longing for home
- Go off with a Stalin white-washed version of the past?
- Whereof perhaps, as I long, a time’s recalled internally?
Buddy explains!

The straight part
We know that "longing for the past" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case longing for the past = nostalgia.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 NOSTALGIA mean?
NOSTALGIA noun- A longing for home or familiar surroundings; homesickness.
- A bittersweet yearning for the things of the past.
- Reminiscence of the speaker's childhood or younger years.