waning

Short definition from Wiktionary

Verb

1. 1
   present participle and gerund of wane

Adjective

1. 1
   Becoming weaker or smaller.
2. 2
   Of the lunar phase: as it shrinks when viewed from the Earth.

Noun

1. 1
   The fact or act of becoming less or less intense or present; fading.
2. 2
   The fact or act of becoming smaller.