The Collaborative International Dictionary
Thirdings
Thirdings \Third"ings\, n. pl. (Eng. Law) The third part of the corn or grain growing on the ground at the tenant's death, due to the lord for a heriot, as within the manor of Turfat in Herefordshire.
Wiktionary
thirdings
n. (context UK legal English) One third of the corn or grain growing on the ground at the tenant's death, paid to the lord as a heriot.