This form of #1943 used only in this one verse and does appear to imply a "cover over/on"....
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uses W-H Ms
Romans 4:7 Happy-ones whom were pardoned/afeqhsan <863> (5681) the lawlessnesses and of whom were covered over/
ep-ekalufqhsan <1943> (5681) the sins.
Textus Rec.) Romans 4:7 makarioi wn afeqhsan ai anomiai kai wn
ep-ekalufqhsan ai amartiai
1943. epikalupto ep-ee-kal-oop'-to from 1909 and 2572; to conceal, i.e. (figuratively) forgive:--cover.
1909. epi ep-ee' a primary preposition; properly, meaning superimposition (of time, place, order, etc.), as a relation of distribution (with the genitive case),
2572. kalupto kal-oop'-to akin to 2813 and 2928; to cover up (literally or figuratively):--cover, hide.
863. aphiemi af-ee'-ay-mee from 575 and hiemi (to send; an intensive form of eimi, to go); to send forth, in various applications (as follow):--cry, forgive, forsake, lay aside, leave, let (alone, be, go, have), omit, put (send) away, remit, suffer, yield up.