Think
Old English thencan, of Germanic origin; related to Dutch and German denken .
wiktionary
From Middle English thinken, thynken, thenken, thenchen, from Old English þenċan, þenċean(“to think”), from Proto-Germanic *þankijaną(“to think, suppose, perceive”), from Proto-Indo-European *teng-(“to think, feel, know”). Cognate with Scots think, thynk(“to think”), North Frisian teenk, taanke, tanke, tånke(“to think”), Saterland Frisian toanke(“to think”), West Frisian tinke(“to think”), Dutch denken(“to think”), Afrikaans dink(“to think”), Low German denken(“to think”), dinken, German denken(“to think”), Danish tænke(“to think”), Swedish tänka(“to think”), Norwegian Bokmål tenke(“to think”), Norwegian Nynorsk tenkja(“to think”), Icelandic þekkja(“to know, recognise, identify, perceive”), Latin tongeō(“know”).
From Middle English thinken, thynken, thenken (also thinchen, thünchen), from Old English þyncan(“to seem, appear”), from Proto-Germanic *þunkijaną(“to seem”). Cognate with Dutch dunken(“to seem, appear”), German dünken(“to seem, appear”), Danish tykkes(“to seem”), Swedish tycka(“to seem, think, regard”), Icelandic þykja(“to be regarded, be considered, seem”). More at methinks.
etymonline
think (v.)
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 (source also of 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 (source also of 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, think, "act of prolonged thinking," is attested by 1834. The figurative thinking cap is attested from 1839.
