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Old English þencan "conceive in the mind, think, consider, intend" (past tense þohte, p.p. geþoht), probably originally "cause to appear to oneself," from Proto-Germanic *thankjan (cf. Old Frisian thinka, Old Saxon thenkian, Old High German denchen, German denken, Old Norse þekkja, Gothic þagkjan); 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 (cf. German dünken, däuchte). Both are from PIE *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." Jocular past participle thunk (not historical, but by analogy of drink, sink, etc.) is recorded from 1876.
v. thought (thôt), think·ing, thinks
To exercise the power of reason, as by conceiving ideas, drawing inferences, and using judgment.
To weigh or consider an idea.
To bring a thought to mind by imagination or invention.
To recall a thought or an image to mind.