The most common and most likely answer to this crossword clue is the 11 letter word BARE-HEADED
I've seen this crossword clue in The Guardian
B
A
R
E
-
H
E
A
D
E
D
Buddy explains!
The straight part
We know that "nothing on top" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case nothing on top = bare-headed.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 BARE-HEADED mean?
BARE-HEADED adjective- Having no covering on the head.
- With no covering on the head.