To think: from Germanic þencan, "to conceive in the mind, to intend, to consider), probably originally "cause to appear to oneself". It also comes from þyncan meaning " to seem or to appear". So the verb means "It seems to me".

USAGE: to think about (to consider seriously bifore making a decision)
To think of (to have formed a possible but not firmly settled plan for)

To refuse: from French refuser, from Latin verb refusare or refundere meaning "pour back, give back". It means that you do not do something that you are asked to do. To decline is very polite and not so firm as refuse.

To reject: from Latin rejectus, past participle of reicere meaning "to throw back". From re- "back" + iacere- "to throw".

To deny: from French denoiir "deny, repudiate, withhold", from Latin denegare "to deny, reject, refuse". From de- "away"+ negare (refuse, say no).