1.
Arrears are amounts of money that you owe, especially regular payments that you should have made earlier.
They have promised to pay the ~ over the next five years...
N-PLURAL
2.
If someone is in ~ with their payments, or has got into ~, they have not paid the regular amounts of money that they should have paid.
...the 300,000 households who are more than six months in ~ with their mortgages.
PHRASE: v-link PHR, PHR after v, oft amount PHR, PHR with/on n
3.
If sums of money such as wages or taxes are paid in ~, they are paid at the end of the period of time to which they relate, for example after a job has been done and the wages have been earned.
Unemployment benefit is paid fortnightly in ~.
PHRASE: PHR after v