'arachnomorph' originates from Greek, specifically the words 'aráchnē' and 'morphē', where 'aráchnē' meant 'spider' and 'morphē' meant 'form'.

'arachnomorph' was formed in Modern English by combining the Greek combining form 'arachno-' (from 'aráchnē') with 'morph' (from 'morphē'), producing a compound meaning 'spider-form'; the plural 'arachnomorphs' follows regular English pluralization.

Initially, the components meant 'spider' + 'form', and the compound retained the sense 'having the form of a spider'; over time it has been used mainly as a descriptive or fictional term for spider-like beings.