'annectant' originates from Latin, specifically the Medieval/Neo-Latin present participle 'annectans' from the verb 'annectere', where the prefix 'an-' (from 'ad-') meant 'to, toward' and 'nectere' meant 'to bind' or 'to tie'.

'annectant' changed from Medieval/Neo-Latin 'annectans' and was adopted into English as a learned/technical word (via Neo-Latin usage) to mean something that connects or binds.

Initially, it meant 'binding to' or 'attaching', but over time it evolved into its current sense of 'serving to connect; linking or joining things'.