Fromslow +‎back.

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slowback (pluralslowbacks)

1. (archaic,slang) Alubber; anidle fellow; aloiterer.
   • 1619,John Favour,Antiquitie triumphing over Noveltie:

     Theslowbacks and lazie bones will none of this

“slowback”, inWebster’s Revised Unabridged Dictionary, Springfield, Mass.:G. & C. Merriam,1913,→OCLC.

• low backs