Willing engineers take day off (5)
I believe the answer is:
ready
'willing' is the definition.
(similar in meaning)
'engineers take day off' is the wordplay.
'engineers' becomes 're' (Royal Engineers).
'take' is a charade indicator (letters next to each other).
'off' indicates anagramming the letters.
'day' is an anagram of 'ady'.
're'+'ady'='READY'
(Other definitions for ready that I've seen before include "Fully prepared" , "Prepare < dough" , "In addition" , "bread" , "Willing (to do something); cash" .)