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' (abbreviation for Royal Engineers).
'take' says to put letters next to each other.
'off' is an anagram indicator.
'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" .)