The Spanish adverb 'imaginariamente' (meaning 'imaginarily') comes from combining the adjective 'imaginario' ('imaginary') with the adverbial suffix '-mente'. The suffix '-mente' itself comes from the Latin word 'mens, mentis' meaning 'mind', and is used in Spanish to form adverbs from adjectives, similar to how '-ly' works in English.

Going further back, 'imaginario' comes from Latin 'imaginarius' ('imaginary'), which was derived from 'imago' ('image, copy'). This shows how the concept of something being imaginary is closely tied to the idea of images or representations in the mind.

Several common Spanish words share this etymology, including: 'imagen' (image), 'imaginar' (to imagine), and 'imaginario' (imaginary). All these words preserve the core meaning related to mental pictures or representations. The adverb 'imaginariamente' simply adds the '-mente' suffix to express how an action is done in an imaginary way.

English speakers can easily connect this word to several familiar English words that share the same Latin root 'imago': 'image', 'imagine', 'imaginary', and 'imagination'. The parallel between Spanish '-mente' and English '-ly' is also helpful - just as 'imaginarily' is formed in English by adding '-ly' to 'imaginary', Spanish forms 'imaginariamente' by adding '-mente' to 'imaginario'.