This phonetical change occured in Ancient Greek. For example, the root helio- "sun" stems from earlier sawelio-. This change also occured in French, for example

This phonetical change occured in Ancient Greek. For example, the root helio- "sun" stems from earlier sawelio-. This change also occured in French, for example, the French word for "forest" is now pronounced without -s- and at some point it had -h-. This sound change occured in Sanskrit, where final -s became -h It's called debuccalization and it's very common in many languages.