Pertaining to a period before the time of which there is a written record.

史前的。

Of, or relating to a language in a period of its development from which contemporary records of its actual sounds and forms have not been preserved.

【语言】未有纪录的(指语言的一个发展阶段，此阶段中语言的音及形尚未有纪录)。

Same as prehistorical.

亦可作 prehistorical。