Early Quenya
qelet
noun. corpse
qeletya-
verb. to rot
kaivo
noun. corpse
Beware, older languages below! The languages below were invented during Tolkien's earlier period and should be used with caution. Remember to never, ever mix words from different languages!
A verb appearing as ᴱQ. qeletya “rot (intr.)” in the Qenya Lexicon with past tense qeleksine- and thus probably related to ᴱQ. qelet (qelekt-) “corpse”, both under the same early root ᴱ√QELE “perish, die, decay, fail” (QL/76). The present tense form of the verb therefore probably involves the sound change of ky > ty.
Neo-Quenya: Since ᴹQ. qelet “corpse” < ᴹ√KWEL appears in Tolkien’s later writings, I would retain ᴺQ. queletya- “to rot” as well.