The most common and most likely answer to this crossword clue is the 10 letter word HIBERNATED
I've seen this crossword clue in The Sunday Telegraph
H
I
B
E
R
N
A
T
E
D
Buddy explains!

The straight part
We know that "Lay dormant till spring" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lay dormant till spring = hibernated.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 HIBERNATED mean?
HIBERNATED verb- To spend winter time in hibernation.
- To live in seclusion.
- To enter a standby state which conserves power without losing the contents of memory.