ETYMOLOGICAL RESEARCH

to think
Old English. þencan "conceive in the mind, think, consider, intend", probably originally "cause to appear to oneself," from Proto-Germanic. *thankjan ; Old English þencan is the causative form of the distinct Old English verb þyncan "to seem or appear" (past tense þuhte, past participle. geþuht), from Proto-Germanic *thunkjan. Both are from Proto-Indo-Eurepean *tong- "to think, feel" which also is the root of thought and thank. The two meanings converged in Middle English and þyncan "to seem" was absorbed, except for archaic methinks "it seems to me."

to deny
early 14th century, from Old French. denoiir "deny, repudiate, withhold," from Clasical Latin denegare "to deny, reject, refuse", from de- "away" + negare "refuse, say 'no,' " from Old Latin nec "not," from Italic base *nek- "not," from Proto-Indo-European base *ne- "no, not"

to reject
early 15th century, from classical Latin rejectus, past participle of reicere "to throw back," from re- "back" + -icere, combining form of iacere "to throw". The noun is first recorded 1550s; rare before 20century

to refuse
century1300, from Old French refuser (12th century), from vulgar Latin refusare.