The difference between arrears and repeat

is that “arrears” is towards the rear, backwards. [14th-16th c.] and “repeat” is to do or say again.

arrears

She, having well before approoved / The feends to be too cruell and severe, / Observ’d th’ appointed way, as her behooved, / Ne ever did her ey-sight turne arere […].
In case the annuity should be arrear for sixty days being lawfully demanded, then the trustee might enter upon the premises assigned […].

I have a large arrear of letters to write.
My own work, with its manifold arrears, took me all day to clear off.
After World War II it took time to clear up the arrears of track maintenance on both lines and it was not until 1953 that the L.M.R. restored any two-hour schedules, the W.R. following suit a year later.

(transitive) To do or say again (and again).
(transitive, medicine, pharmacy) To refill (a prescription).
(intransitive) To happen again; recur.
(transitive) To echo the words of (a person).
(intransitive) To strike the hours, as a watch does.
(obsolete) To make trial of again; to undergo or encounter again.
(law, Scotland) To repay or refund (an excess received).
(procedure word, military) To call in a previous artillery fire mission with the same ammunition and method either on the coordinates or adjusted either because destruction of the target was insufficient or missed.
To commit fraud in an election by voting more than once for the same candidate.

The scientists repeated the experiment in order to confirm the result.
When this conversation was repeated in detail within the hearing of the young woman in question, and undoubtedly for his benefit, Mr. Trevor threw shame to the winds and scandalized the Misses Brewster then and there by proclaiming his father to have been a country storekeeper.
Their rationale with repeating me was that the prior program had not been of sufficient quality to teach me the error of my ways.
Add 100, left 50. Repeat, over.
Use “say again” instead of repeat on the radio. Repeat will bring in artillery fire.

An iteration; a repetition.
A television program shown after its initial presentation; a rerun.
(medicine, pharmacy) A refill of a prescription.
(genetics, biochemistry) A pattern of nucleic acids that occur in multiple copies throughout a genome (or of amino acids in a protein).
(music) A mark in music notation directing a part to be repeated.