This is the 759th most frequent Japanese word.
なかろ
"なかろ" is a classical or old-fashioned negative form meaning "probably not" or "will not be."
Used to express probability in negative form.
彼は何も言わなかろう。
He will probably say nothing.
Indicates a probable negative future occurrence.
明日は雨は降らなかろう。
It probably won't rain tomorrow.
Used with an additional verb (思う) for supposition of negative probability.