From a primary steibo (to "step" or "stamp"); a spread (as if tramped flat) of loose materials for a couch, i.e. (by implication) a bough of a tree so employed -- branch.
a. a spread or layer of leaves, reeds, rushes, soft leafy twigs, straw, etc., serving for a bed (Hesychius στιβάς. ἀπό ῤάβδων ἡ χλωρῶν χορτων στρωσις καί φυλλων); so in Greek writings from Herodotus down.
b. that which is used in making a bed of this sort, a branch full of leaves, soft faliage: so Mark 11:8 L T Tr WH for στοιβάδας, an orthographical error (see Tdf.'s note at the passage). STRONGS NT 4746: στοιβάςστοιβάς, στοιβαδος, ἡ, see στιβάς, b.