Prompt about fixing day (5)
I believe the answer is:
ready
'prompt' is the definition.
(similar in meaning)
'about fixing day' is the wordplay.
'about' becomes 're' ('re' means regarding or about).
'fixing' indicates an anagram.
'day' anagrammed gives 'ady'.
're'+'ady'='READY'
(Other definitions for ready that I've seen before include "Intelligent" , "Willing (to do something), prepare" , "Poised for action" , "bread" , "Prompt and adequate" .)