Spank (, v. t. [imp. & p. p. Spanked (; p. pr. & vb. n. Spanking.]
Etymology: [Of unknown origin; cf. LG. spakken, spenkern, to run and spring about quickly.]
To strike, as the breech, with the open hand; to slap.
2 other Webster entries under this spelling
Spank, n.
A blow with the open hand; a slap.
Spank, v. i.
To move with a quick, lively step between a trot and gallop; to move quickly. Thackeray.
Shades of meaning
Fernald has no entry of its own for spank; he lists it under beat.
He lists it without comment; the entries above explain its neighbors.