似乎沒看出太大差別：

pro·fi·cient
(pr?-f?sh′?nt)
adj.
Having or marked by an advanced degree of competence, as in an art, vocation, profession, or branch of learning.
n.
A person who exhibits such competence; an expert.


a·dept
(?-d?pt′)
adj.
Very skilled or accomplished. See Synonyms at proficient.
n. (?d′?pt′)
A highly skilled person; an expert: "political consequences in getting rid of all the skeptics, unbelievers, and adepts of rival faiths" (Gene Lyons).