The most common and most likely answer to this crossword clue is the 11 letter word NAMBY-PAMBY
I've seen this crossword clue in The Guardian
N
A
M
B
Y
-
P
A
M
B
Y
Buddy explains!

The straight part
We know that "Weak/Weak" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case weak/weak = namby-pamby.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 NAMBY-PAMBY mean?
NAMBY-PAMBY noun- One who is insipid, sentimental or weak.
- Talk or writing which is weakly sentimental or affectedly pretty.
- To coddle.
- Insipid and sentimental.
- Lacking vigor or decisiveness; spineless; wishy-washy.