An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1a) No longer in general use; fallen into disuse.
1b) Biology: (of a living organism) Reduced to a redument, or completely lacking, as compared with a corresponding part in related organisms.
2) To make obsolete by replacing with something newer or better.

From L. obsoletus "grown old, worn-out," p.p. of obsolescere "fall into disuse, be forgotten about, become tarnished," which probably is from ob "away" + an expanded form of solere "to be used to, be accustomed."

Pitâr, from Tabari pitâr "worn out," specifically "rotten tree," pitə-pât "anything worn out or useless," from pit, variant of Pers. pud "worn out, decayed," pusidan/pus- "to rot," cf. Pashto puda, Wakhi pitk "rotten, foul," Kurd. (Kurm.) puc "rotten, useless;" Av. pu- "to stink, rot," akin to Gk. puos, L. pus "pus."