logamnesia (noun) – a loss of ability to speak or understand language, also known as selective aphasia
BREAKDOWN: LOG- (word, speech) + A- (no, without) + MNE- (memory) + -IA (state of)
This word is built on the root MNE-, which means memory or to remember.
Common MNE- words include amnesia.
More esoteric MNE- words include dysmnesia and mneme.