PIE *nogw「裸」から。語源はヌード、体育館。
Which thou must (though it grieve thee) grantPhrase naked as a jaybird (1943) was earlier naked as a robin (1879, in a Shropshire context); the earliest known comparative based on it was naked as a needle (late 14c.). Naked eye is from 1660s, unnecessary in the world before telescopes and microscopes.
I trumped never a man.
But truely told the naked trueth,
To men that meld with mee,
For neither rigour, nor for rueth,
But onely loath to lie.
[Montgomerie, 1585]