thinkyoudaoicibaDictYouDict[think 词源字典]
think: [OE] Think goes back to an Old English thencan. This was a variant of thyncan ‘seem, appear’, which survives in the archaic methinks (literally ‘it seems to me’), and so etymologically think probably carries the notion of ‘causing images, reflections, etc to appear to oneself, in one’s brain’. The noun thought comes from the same prehistoric Germanic base as produced the verb (as does English thank). Related Germanic forms include German and Dutch denken, Swedish tänka, and Danish tænke.
=> thank, thought[think etymology, think origin, 英语词源]
think (v.)youdaoicibaDictYouDict
Old English þencan "imagine, conceive in the mind; consider, meditate, remember; intend, wish, desire" (past tense þohte, past participle geþoht), probably originally "cause to appear to oneself," from Proto-Germanic *thankjan (cognates: 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, to appear" (past tense þuhte, past participle geþuht), from Proto-Germanic *thunkjan (cognates: German dünken, däuchte). Both are from PIE *tong- "to think, feel" which also is the root of thought and thank.

The two Old English words converged in Middle English and þyncan "to seem" was absorbed, except for its preservation in archaic methinks "it seems to me." As a noun, "act of prolonged thinking," from 1834. The figurative thinking cap is attested from 1839.