Origin and history of thoughtful

"act or product of mental activity," Old English þoht, geþoht "process of thinking, a thought; compassion," from stem of þencan "to conceive of in the mind, consider" (see think). Cognate with the second element in German Gedächtnis "memory," Andacht "attention, devotion," Bedacht "consideration, deliberation."

Bammesberger ("English Etymology") explains that in Germanic -kt- generally shifted to -ht-, and a nasal before -ht- was lost. Proto-Germanic *thankija- added a suffix -t in the past tense. By the first pattern the Germanic form was *thanht-, by the second the Old English was þoht.

OED quotes both Walt Whitman and Emily Dickinson spelling it thot. A minor or inferior one in 19c. might be a thoughtlet (1846), thoughtling (1848), or thoughtkin (1867),

Second thought "later consideration" is recorded from 1640s. Thought-crime is from "Nineteen Eighty-Four" (1949); thought police is attested from 1945, originally in reference to war-time Japanese Special Higher Police (Tokubetsu Koto Keisatsu).

I do not wish to be any more busy with my hands than is necessary. My head is hands and feet. I feel all my best faculties concentrated in it. My instinct tells me that my head is an organ for burrowing, as some creatures use their snout and fore-paws, and with it I would mine and burrow my way through these hills. I think that the richest vein is somewhere hereabouts ; so by the divining rod and thin rising vapors I judge ; and here I will begin to mine. ["Walden"]

"wanting thought," in various senses; 1590s, "heedless, imprudent, done without thought," from thought + -less. It is attested by 1680s as "dull-witted." The meaning "inconsiderate of others" is perhaps from 1794. Related: Thoughtlessly; thoughtlessness.

word-forming element attached to nouns (and in modern English to verb stems) and meaning "full of, having, characterized by," also "amount or volume contained" (handful, bellyful); from Old English -full, -ful, which is full (adj.) become a suffix by being coalesced with a preceding noun, but originally a separate word. Cognate with German -voll, Old Norse -fullr, Danish -fuld. Most English -ful adjectives at one time or another had both passive ("full of x") and active ("causing x; full of occasion for x") senses.

It is rare in Old English and Middle English, where full was much more commonly attached at the head of a word (for example Old English fulbrecan "to violate," fulslean "to kill outright," fulripod "mature;" Middle English had ful-comen "attain (a state), realize (a truth)," ful-lasting "durability," ful-thriven "complete, perfect," etc.).