The most common and most likely answer to this crossword clue is the 6 plus 6 letter word COMPOS MENTIS
C
O
M
P
O
S
M
E
N
T
I
S
More clues leading to the result COMPOS MENTIS
- People in a heap in the garden: one’s sane
- Rotter is gathering people together
- Smothering people in manure is rational
- Rotter is binding pieces together
- MPs’ incomes to get reformed? That’s sound
- Having gathered pieces, dress is all there
- All there is after remark about rejected bribe
- Not a screwball sitcom, funny about heartless men of letters
- Capable of reasoning that source of money coming in stops income varying
- Opinion about potty son, one’s all there
Buddy explains!
The straight part
We know that "all there" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case all there = compos mentis.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.