Both Uses of

scythe
in
A Storm of Swords

They were armed with spears and fire-hardened lances, all but their leader, a fleshy blond man with watery eyes who bore a great curved scythe of sharpened steel.†
p. 93.8

scythe = a tool for cutting grass that has a curved blade and a long handle that is held with both hands

The fat Dothraki put aside his knife to unsheathe a huge curved arakh, the wickedly sharp scythe-sword the horselords loved.†
p. 297.6 *

Definitions:

(1) (scythe)
a tool for cutting grass that has a curved blade and a long handle that is held with both hands

(See this Google Images link for scythe to see samples.)
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

Much more rarely, scythe can be used as a verb to reference the cutting of weeds or tall grasses (such as hay or wheat) with a scythe. Metaphorically, the verb form can be used to describe cutting through anything as in "scythed through the problems in less than a week."