The Spanish verb 'echar' (meaning 'to throw' or 'to cast') comes from the Latin verb 'iactare', which meant 'to throw repeatedly'. 'Iactare' itself was derived from the simpler Latin verb 'iacere' meaning 'to throw'. 'Iactare' was what's called a frequentative form of 'iacere', meaning it expressed repeated action. As the word evolved from Latin to Spanish, the initial 'i' sound transformed into 'e' and the 'ct' cluster simplified to 'ch', giving us the modern Spanish 'echar'.

Some related Spanish words include 'yacente' (lying down) and 'yacer' (to lie), which come from the same Latin root 'iacere'. While 'echar' maintained the meaning of throwing or casting, these related words developed to focus more on the position or state that results after something has been cast down.

Several English words are related to 'echar' through the Latin root 'iacere', including 'eject', 'inject', 'project', and 'jet'. All these words maintain some connection to the original meaning of throwing or casting: 'eject' means to throw out, 'inject' to throw in, 'project' to throw forward, and a 'jet' is something that's thrown or shot forth (like water or air). The 'ject' part in these words comes from the past participle of 'iacere'.