A (plural) pronominal form of ᴹQ. sem(p)- appearing in Demonstrative, Relative, and Correlative Stems (DRC) from 1948 (PE23/103). Its adjective form is sempa (PE23/106). In drafts Tolkien gave it a singular form sempe (PE23/106 note #80).
Qenya
manka-
verb. to trade
sempi
pronoun. few
A verb given as ᴹQ. {mahta- >> māka- >>} manka- “trade” in The Etymologies of the 1930s under the root ᴹ√MBAKH “exchange” (Ety/MBAKH).