In American English, dependent is (1) an adjective meaning contingent on another, and (2) a noun meaning a person who is financially supported by someone else. Dependant is a rare alternative spelling with no definitions of its own.
According to every British reference resource we checked, British English treats dependant as the noun and dependent as the adjective.1 2 3 We do find the distinction borne out in real-world usage, but it’s by no means consistent. Both spellings regularly appear as both nouns and as adjectives.
We checked the Guardian and Daily Telegraph style books (because they’re available online, not because they’re the most authoritative), and both make the distinction, saying dependant is the noun and dependent the adjective.4 5 Yet Google site searches reveal that neither of these publications consistently follows its own style policy. Both tend to keep the words separate, but exceptions abound.
Let’s look at a few examples from British publications:
Polymetal’s prospectus concedes how dependant the company is on Mr Kerimov. [Independent]
There is also likely to be a curb on the number of dependents they can bring with them. [Guardian]
Older people don’t want to become dependant, but councils need to help them help themselves. [Telegraph]
Parents could spend more time with their children or other dependents. [Daily Mail]