'aphasic' originates from English (formed in the late 19th century) from the noun 'aphasia' plus the adjectival suffix '-ic'; 'aphasia' itself comes from Greek.

'aphasia' comes from Greek ἀφασία (aphasía), from a- 'without' + phásis 'speech' (related to phēmi 'to speak'); the English adjective 'aphasic' derived from 'aphasia', and the plural noun 'aphasics' developed to refer to people with aphasia.

Initially the Greek root conveyed the idea 'without speech'; over time it became a medical term 'aphasia' for loss of language function, and 'aphasic' came to mean 'relating to aphasia' or 'a person with aphasia'.