The most common and most likely answer to this crossword clue is the 8 letter word TONSURED
I've seen this crossword clue in The Daily Telegraph
T
O
N
S
U
R
E
D
More clues leading to the result TONSURED
Buddy explains!

The straight part
We know that "having nothing on top" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case having nothing on top = tonsured.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 TONSURED mean?
TONSURED verb- To shave the crown of the head as a sign of humility and religious vocation.