skillful (adj.)

early 12c., "knowledge, divine wisdom;" late 12c., "power of discernment, sound judgment; that which is reasonable," senses all now obsolete, from Old Norse skil "distinction, ability to make out, discernment, adjustment," which is related to skilja (v.) "to separate; discern, understand," from Proto-Germanic *skaljo- "divide, separate" (source also of Swedish skäl "reason," Danish skjel "a separation, boundary, limit," Middle Low German schillen "to differ," Middle Low German, Middle Dutch schele "separation, discrimination;" from PIE root *skel- (1) "to cut").

The sense of "practical knowledge and ability, cleverness" is recorded by early 13c.

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.).

also unskilful, late 14c., "foolish," from un- (1) "not" + skillful (adj.). Meaning "inexpert" is from 1560s. Related: Unskillfully.