adverb
Expresses that something happens or is the case for an unclear or unspecified reason. Often used when the speaker cannot pinpoint the cause.
何とやら今日は気分がすぐれない。
For some reason I don't feel well today.
何とやら彼の話は信用できない気がする。
Somehow I feel I can't trust what he says.
expression
whatsitsname; what-you-call-it; Mr. so-and-so
Used as a placeholder when the speaker cannot recall or does not want to specify a name or term. Often appears in the pattern ～とか何とやら.
あの、何とやらさんがまた来てたよ。
That, what's-his-name, was here again.
新しい企画とか何とやらで忙しいらしい。
He seems busy with a new project or what-you-call-it.
expression
Follows a noun or phrase to imply there are other similar things left unmentioned. Similar to など, but more colloquial and often used when the speaker is being vague.
彼は仕事がどうの、給料が何とやらと文句ばかり言っている。
He's always complaining about his work, his salary, and so on.
最近は健康が何とやらで、ジムに通い始めた。
Lately, with health and all that, I started going to the gym.