adverb
A formal, somewhat literary adverb used to express a strong wish or hope, often at the beginning of a sentence. Equivalent to 願わくは.
See also: 願わくは
願わくば、この計画が成功しますように。
I pray that this plan will succeed.
願わくば、皆様のご協力
I sincerely hope for your cooperation.
願わくは is an older, more classical form with the same meaning; 願わくば is the modern variant.
Derived from the classical Japanese expression 願わくは (negawaku wa), where 願わく is the attributive form of the verb 願う (negau, 'to wish') and は is the topic particle. The modern form 願わくば replaces は with ば, possibly influenced by the conditional or by analogy with other adverbial expressions.