Formation of word "何となく"

Question

I think, the word "何となく" means as below

somehow or other; for some reason or another;

However, how it has been formed so that it means like above?

Answer 1

何となく is made up of:

• 何【なん】と: contraction of...
  • 何【なに】: question-word "what"
  • と: quotative particle "(call/say) that"
• なく: adverbial form of i-adjective ない ("not be"); "not being, without"

As a whole it means "without 'what'", or in more understandable English "without naming what (it is)", thus comes to represent a feeling that you can't pinpoint the specific reason.

Note that this phrase is already an idiom, with an undivided accent なんとなく{LHHHL} instead of etymological なんと{HLL}なく{HL}.

Similar constructions:

• それとなく "without (pointing) 'that'" → "implicitly; subtly"
• 幾度／何度となく "without 'how many times'" → "countless times"
• ～ともなく "without any specific" (a JLPT N1 grammar)