Obligation - Crossword Clue, Answer and Explanation

'obligation' is the definition.
(I know that obligation can be written as duty)

This is the entire clue.

(Other definitions for duty that I've seen before include "Levy - tax on imports" , "Service - tax - office" , "Not subject to customs tax" , "A tax; compulsory task" , "assignment" .)

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

'obligation' is the definition.
(I've seen this in another clue)

This is all the clue.

(Other definitions for onus that I've seen before include "'Responsibility, task or burden (4)'" , "Encumbrance" , "'Burden, load (4)'" , "Responsibilty" , "Liability" .)

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

'obligation' is the definition.
(I know that debt is a type of obligation)

This is the entire clue.

(Other definitions for debt that I've seen before include "Money owed or due" , "Something owed" , "Arrears, liability" , "What's due" , "outstanding" .)

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

Obligation (4)