A noun in 1970 green-ink revisions to Outline of Phonology (OP2) derived from ✶arp(h)ō “seizer, thief” based on the root √RAPH “seize, grab” (PE19/89).
Quenya
arpo
thief
arpo
noun. seizer, thief
arpo
noun. thief
thief
pilu
thief, robber
pilu noun "thief, robber" (QL:73)
arpo noun "thief" (PE19:89)