noun
multiplying by one; original amount
Mathematical sense: multiplying by one, i.e., the same amount. Often used in contexts like 元の一倍 (the original amount).
この値段は元の一倍です。
This price is the same as the original.
adverb
Used adverbially in the fixed expression 人一倍 (more than others, exceptionally). Not used as a standalone adverb.
See also: 人一倍
彼は人一倍努力した。
He made an extra effort, more than anyone else.
noun
double; twice as much; twofold
Dated usage meaning 'double'. In modern Japanese, 二倍 is standard for 'double'. 一倍 now usually means 'same amount'.
See also: 二倍
昔は「一倍」が「二倍」の意味で使われた。
In the past, 一倍 was used to mean 'double'.