plat (n.) Look up plat at Dictionary.com
"piece of ground," 1510s, a variant of plot (n.) assimilated to Middle English plat (adj.) "flat," which is from Old French plat "flat, stretched out" (see plateau (n.)). See OED for full explanation.
plat (v.) Look up plat at Dictionary.com
"to interweave," late 14c., variant of plait (v.). Related: Platted; platting.