The unglossed headword is an abstract noun expressing quality: "thrown-to-the-ground-ness". Its only other attestation is in Iamblichus, Protrepticus 116.10 (accusative case there), which has perhaps generated this Suda entry.
[1] Likewise or similarly in other lexica. If xamaipeth/s is quoted from somewhere, extant possibilities begin with Plato, Symposium 203D.