Work hard - Crossword Clue, Answer and Explanation

'work hard' is the definition.
(slog can mean to work very hard)

This is the entire clue.

(Other definitions for slog that I've seen before include "Work doggedly" , "Hit hard - hard trek" , "big hit" , "Hit out without style" , "almighty wallop" .)

I've seen this clue in the USA Today, The Telegraph, The New York Times, the Newsday, the Universal, the LA Times, The Star Tribune, the Sydney Morning Herald, The Mirror, the Penny Press, The Guardian and the King Feature Syndicate.

'work hard' is the definition.
(I've seen this before)

This is all the clue.

(Other definitions for labour that I've seen before include "Productive work" , "unnecessarily elaborate" , "21 [PARTY] ?" , "Workers" , "Painful time" .)

I've seen this clue in the Penny Press and The Mirror.

(Other definitions for knuckle down that I've seen before include "Use some application" , "Apply oneself to hard work" , "Joint not working" , "Begin serious work" , "Apply oneself seriously" .)

I've seen this clue in The Times and The Mirror.

Work hard (4)