Sad at having made a mess of a sitter? (6)
I believe the answer is:
triste
'sad' is the definition.
(I've seen this in another clue)
'of a sitter?' is the wordplay.
'of' indicates an anagram (the answer comes from or 'of' the letters).
'sitter' with letters rearranged gives 'TRISTE'.
'at having made a mess' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for triste that I've seen before include "Sad (arch)" , "Old word for sad" , "Valse -- (Sibelius)" , "Sad in France" .)