Word Study
obsolescent
CIDE DICTIONARY
obsolescent, a. [L. obsolescens, -entis, p. pr. of obsolescere, to wear out gradually, to fall into disuse; ob (see Ob-) + solere to use, be wont.].
Going out of use; becoming obsolete; passing into desuetude. [1913 Webster]
OXFORD DICTIONARY
obsolescent, adj. becoming obsolete; going out of use or date.
Derivative
obsolescence n.
Etymology
L obsolescere obsolescent- (as OB-, solere be accustomed)
For further exploring for "obsolescent" in Webster Dictionary Online