person who longs for something; desirer; luster
A somewhat literary or formal noun for someone who intensely desires or craves something. 'Luster' is an archaic or rare sense; modern usage focuses on strong longing.
He is a seeker of truth.
A luster after power is never satisfied.
Compound of 渇望 (katsubō, 'craving, longing') + 者 (sha, 'person'). The derivation is straightforward; the word is not commonly listed in etymological references.