The Spanish adverb 'mentalmente' (meaning 'mentally') comes from combining two elements: the adjective 'mental' and the adverbial suffix '-mente' (meaning 'in a manner'). The adjective 'mental' derives from Latin 'mentalis' meaning 'of the mind', which itself was formed from the Latin noun 'mens' (meaning 'mind') and the Latin suffix '-alis' (meaning 'relating to').

This formation follows a common pattern in Spanish where '-mente' is added to the feminine form of an adjective to create an adverb, similar to how English uses '-ly'.

Some related simpler Spanish words include 'mente' (mind), 'mental' (mental), and 'mentir' (to lie). While 'mente' and 'mental' have obvious connections to thinking and the mind, 'mentir' comes from the same Latin root but evolved to refer to creating thoughts that aren't true.

English speakers can recognize this word's relationship to many familiar terms like 'mental', 'mentality', and even 'mention' (which originally meant to think of something). The word 'mind' itself, though similar in meaning to 'mens', is not etymologically related as it comes from Germanic origins rather than Latin.