Fleet-footed is an adjective
According to the Merriam Webster online dictionary fleet-footed means: Able to run fast.
This phrase is used on page 89 of my reading when Stamp Paid was explaining to Paul D the events that led up to Sethe attacking her children and killing one of them in the wood shed. Stamp Paid stated, “… because that explained why nobody ran ahead; why nobody sent a fleet-footed son to cut ‘cross a field as soon as they saw the four horses in town….”
Stamp paid was trying to make Paul D understand that although usually a family might send one of their son that ran very fast to take a short cut through nearby fields to warn Sethe, that day no warning was sent this way.