IPA: /ˌsɪn.əˈθiː.zi.ə/
KK: /sɪnəˈθiːzə/
A condition where one sense is simultaneously perceived as if by one or more additional senses, such as seeing colors when hearing music.
She experiences synaesthesia, so when she hears a piano, she sees bright colors.
Synaesthesia → It is formed from "syn-" (meaning together) and "aisthesis" (meaning sensation or perception). The word describes a condition where one sense is simultaneously perceived as if by one or more additional senses, hence the idea of sensations being experienced together.
Think of senses that are experienced 'together' ('syn-') — that's what synaesthesia means, where one sensation triggers another.