Soqotri

ṭáham - to grow old (of things) (LS 200, CSOL II 616)

Proto-MSA
*ṭhm - to vanish (Kogan 2015:574)

The origin is uncertain. Note perhaps Arb. ˀal-muṭahham- = ˀal-qalīlu laḥmi l-waǯhi (LA 12 432). (Kogan 2015:574)