Origin and history of thought-out

expressing motion or direction from within or from a central point, also removal from proper place or position, Old English ut "out, without, outside," from Proto-Germanic *ūt- (Old Norse, Old Frisian, Old Saxon, Gothic ut, Middle Dutch uut, Dutch uit, Old High German uz, German aus), from PIE root *uidh- "up, out, up away, on high" (source also of Sanskrit ut "up, out," uttarah "higher, upper, later, northern;" Avestan uz- "up, out," Old Irish ud- "out," Latin usque "all the way to, continuously, without interruption," Greek hysteros "the latter," Russian vy- "out").

Sense of "to a full end, completely, to a conclusion or finish" is from c. 1300. Meaning "so as to be no longer burning or alight; into darkness" is from c. 1400. Of position or situation, "beyond the bounds of, not within," early 15c. Meaning "into public notice" is from 1540s; that of "away from one's place of residence," c. 1600. The political sense of "not in office, removed or ejected from a position" is from c. 1600. Meaning "come into sight, become visible" (of stars, etc.) is by 1610s. In radio communication, a word indicating that the speaker has finished speaking, by 1950.

As a preposition, "out of; from, away from; outside of, beyond; except; without, lacking;" mid-13c., from the adverb.

Meaning "from harmonious relations, into quarreling" (as in to fall out) is from 1520s. Meaning "from one's normal state of mind" (as in put out) is from 1580s; out to lunch "insane" is student slang from 1955. Adjectival phrase out-of-the-way "remote, secluded" is attested from late 15c. Out-of-towner "one not from a certain place" is from 1911. Out of this world "excellent" is from 1938; out of sight "excellent, superior" is from 1891. To (verb) it out "bring to a finish" is from 1580s. Expression from here on out "henceforward" is by 1942. Out upon, expressing abhorrence or reproach, is from early 15c.

Middle English thinken, a convergence of two Old English verbs from the same prehistoric source but with distinct forms and senses.

Thinken (1) "present the appearance of (something)" is from Old English þyncan, þincan. Thinken (2), "exercise the faculty of reason, cogitate" is from Old English þencan. Grammatically, þencan is the causative form of þyncan. The two converged in form in Middle English and the sense from þyncan "to seem" was absorbed or lost but is preserved in methinks "it seems to me."

The sense of "say to oneself mentally" (thinken (2)) was in 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 *thankjanan (source also of Old Frisian thinka, Old Saxon thenkian, Old High German denchen, German denken, Old Norse þekkja, Gothic þagkjan).

Old English þyncan "to seem, to appear" (past tense þuhte, past participle geþuht) is the source of Middle English thinken (1). It is reconstructed to be from Proto-Germanic *thunkjan (source also of German dünken, däuchte).

Both are from PIE *tong- "to think, feel" (Watkins), which also is the root of thought and thank. Boutkan gives this no IE origin, rejects proposed cognates, and suggests a substrate source.

Thinken (1) in Middle English also could mean "seem erroneously or falsely" or "seem fitting or proper." It often was used impersonally, with an indirect object, as in methinks.

To think twice "hesitate, reconsider" is by 1898; to think on one's feet "adjust quickly to changing circumstances" is by 1935; to think so "be of that opinion" is by 1590s; to think (something) over "give continued thought to" is by 1847. To think up "invent, make up, compose" is from early 15c. Modern use might be 19c. I tink, representing dialectal or foreign pronunciation of "I think," is by 1767.