Obsolescent, a.
Etymology: [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.
Shades of meaning
Fernald has no entry of its own for obsolescent; he lists it under obsolete.
He lists it without comment; the entries above explain its neighbors.