From Longman Dictionary of Contemporary Englishset somebody/something against somebody/something phrasal verb1 AGAINST/OPPOSEto make someone start to fight or quarrel with another person, especially a person who they had friendly relations with before The bitter civil war set brother against brother.2 set yourself against (doing) something to decide that you are opposed to doing or having something She’s set herself against going to university.3 set something against taxPET to officially record the money you have spent on something connected with your job, in order to reduce the amount of tax you have to pay → set→ See Verb table
Examples from the Corpus
set against • Yours sincerely Dear I am returning your invoice because I do not have an order form to set it against.• There is particular concern that an informant may try to set police officer against police officer and force against force.• Marina watched him set the rifle against the stairway and climb back up.• I wondered what his thoughts had been when his former comrades set him up against the wall.• Why has the Supreme Court set itself against the will of the majority on such an unprecedented scale?• In short, the Middle East sets true believer against true believer with survival as the issue.• Instead, the earnings in your new job will usually be set off against what you have lost.• Social security benefits will be set off against your loss; the relevant rules are contained in detailed regulations.set yourself against (doing) something• She leaned into him, set herself against him.• But pop sets itself against nature and abandons wisdom for folly, moments of dissipation.• The three Established Church representatives set themselves against; the other four who were Free Churchmen were for it.• Why has the Supreme Court set itself against the will of the majority on such an unprecedented scale?set something against tax• Parents can also set costs against tax.From Longman Business Dictionaryset something against something phrasal verb [transitive] to consider something in relation to another thing, especially when that other thing is more importantAs expenditure is incurred on the account, these debits are set against the credits. → set→ See Verb table 