The most common and most likely answer to this crossword clue is the 11 letter word WISHY-WASHY
W
I
S
H
Y
-
W
A
S
H
Y
Buddy explains!

The straight part
We know that "Feeble" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case feeble = wishy-washy.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 WISHY-WASHY mean?
WISHY-WASHY adjective- Wavering; lacking in commitment, certainty, or support; namby-pamby.
- Thin or watery.