Steal a march, with chief to begin (4,5)
I believe the answer is:
head start
'steal a march' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'with chief to begin' is the wordplay.
'with' says to put letters next to each other.
'chief' becomes 'head' (synonyms).
'to begin' becomes 'start' ('start' can be a synonym of 'begin').
'head'+'start' is 'HEAD START'.
Can you help me to learn more?
(Other definitions for head start that I've seen before include "advantage, initially" , "Advantage gained by beginning early" , "A good beginning using one's loaf" , "An early advantage for the star ad" , "Boost?" .)