Some dictionaries state that this is from earlier ぎこつない (gikotsunai, “blunt, brusque, rough”), with an early citation from 1534, but no further derivation given. The ending ない (-nai) appears to be the regular suffix indicating a quality or state (likely related to verb ending ぬ nu). However, there is no clear etymon for the gikotsu portion.
Meanwhile, there is the now-obsolete classical Japanese adjective 骨無し (kochinashi) of very similar meaning, with citations in the Heian-period book The Tale of Genji. A later form 骨無し (kotsunashi) is dated to the mid-1300s, a couple centuries later. The kanji are likely ateji: the literal meaning of boneless as spelled does not fit the semantics of how this term is used. The -nashi portion is very likely the same -nai adjectival suffix indicating a quality or state, while the kotsu or kochi portions can be found in reduplicative native-Japanese adverbs こちこち (kochikochi, imitative of the sound of ticking, or rattling; also used to describe something moving uneasily due to stiffness or lack of lubrication) and こつこつ (kotsukotsu, imitative of the sound of hard objects striking, such as doors or wooden clogs; also used to describe a person's looks or personality as angular or prickly). However, there is no clear etymon for the gi- portion. It might be an alteration of 気 (ki, “mood, temperament”).
- ぎごちない (gigochinai)
ぎこちない (-i inflection, romaji gikochinai)
- たどたどしい (tadotadoshii)
Gikochinai refers to action that is unrefined and not yet smooth due to lack of practice. Tadotadoshii refers to action that is halting or stumbling due to the actor making mistakes.