The most common and most likely answer to this crossword clue is the 9 letter word PERENNIAL
P
E
R
E
N
N
I
A
L
More clues leading to the result PERENNIAL
- Constant friend outside pub before getting round
- Enduring ring receiving private backing
- In PE learn about constantly growing
- Plan Irene devised is never failing
- Constantly growing burst of laughter welcomes return of Private
- Applying for eternity ring worn by retreating private?
- Endless toll gates turning inward
- Note name assumed by wild alpine plant
Buddy explains!

The straight part
We know that "Constant" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case constant = perennial.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 PERENNIAL mean?
PERENNIAL noun- A perennial plant; a plant that is active throughout the year or survives for more than two growing seasons.
- Lasting or remaining active throughout the year, or all the time.
- (of a plant) Having a life cycle of more than two years.
- Continuing without cessation or intermission; perpetual; never failing.
- Enduring; lasting; timeless.
- Recurrent; appearing or recurring again and again.