Wiktionary
post-lingual deafness
n. The contracting of deafness after acquiring a first language.
Wikipedia
Post-lingual deafness
Post-lingual deafness is a deafness which develops after the acquisition of speech and language, usually after the age of six.
Post-lingual hearing impairments are far less common than prelingual deafness. Typically, hearing loss is gradual, and often detected by family and friends of the people so affected long before the patients themselves will acknowledge the disability.