The Spanish demonstrative pronoun 'aquel' (meaning 'that' or 'that one') comes from Vulgar Latin 'eccum ille', which literally meant 'behold that one'. The first part, 'eccum' (meaning 'behold, here is'), was itself formed from the Latin words 'et' ('and') combined with the deictic particle '-ce' (meaning 'here'). This was then combined with 'ille' (meaning 'that' or 'those') to form the complete demonstrative expression. Over time, this Vulgar Latin phrase evolved phonetically to become 'aquel' in Spanish, while maintaining its demonstrative meaning of pointing to something distant.

The Spanish pronoun 'él' (meaning 'he') is related to 'aquel', as both derive from the Latin 'ille'. While 'aquel' developed from a compound form specifically for demonstrative use, 'él' developed directly from 'ille' as a personal pronoun. The feminine forms 'aquella' and 'ella' show this relationship even more clearly.

While English doesn't have any direct cognates of 'aquel', we can find some related words through the Latin 'ille'. Words like 'else' and 'elastic' ultimately derive from Latin phrases containing forms of 'ille'. Additionally, many English words beginning with 'il-' (when followed by 'l') such as 'illegal', 'illicit', and 'illuminate' contain this same Latin root, though their meanings have diverged significantly from the original demonstrative sense.