The Spanish verb 'juntar' (meaning 'to join' or 'to unite') comes from the Latin verb 'iungere', which had the same meaning of 'to join' or 'unite'. The evolution went through the Latin past participle 'iunctus' ('joined, united'), which developed into the Spanish word 'junto' ('together'). The verb 'juntar' was then formed by adding the common Spanish verb suffix '-ar' to the base 'junto'.

The change from Latin 'iu-' to Spanish 'ju-' is a regular sound change that occurred as Latin evolved into Spanish, making the word easier to pronounce for Spanish speakers.

Several common Spanish words are related to 'juntar'. The most straightforward is the adverb 'junto' meaning 'together', which comes directly from the same Latin root. You might also recognize 'junto a' meaning 'next to' or 'beside'. The adjective 'conjunto' ('joint, combined') is also related, being formed from 'junto' with the prefix 'con-'.

English has many cognates from the same Latin root 'iungere'. The most obvious ones are 'join', 'junction', and 'juncture', all of which preserve the basic meaning of bringing things together. The word 'joint' (as in knee joint or marijuana joint) also comes from this root. Even 'conjugal' (relating to marriage) comes from this root, literally meaning 'joining together'.