ob·so·les·cent 
(ŏb′sə-lĕsənt)
(ŏb′sə-lĕsənt)adj.
1. Being in the process of passing out of use or usefulness; becoming obsolete.
2. Biology Becoming reduced during the course of evolution; vestigial or nearly vestigial. Used of an organ or other part of an organism.
[Latin obsolēscēns, obsolēscent-, present participle of obsolēscere, to fall into disuse : ob-, away; see OB- + solēre, to be accustomed to.]
ob′so·lescence n.
ob′so·lescent·ly adv.