The Spanish word 'siempre' meaning 'always' comes from the Latin word 'semper', which also meant 'always'. The Latin word contained the adverbial suffix '-per'. As Latin evolved into Old Spanish, 'semper' changed to an intermediate form '*siemper', and finally to the modern Spanish 'siempre'. This evolution shows a common sound change where the Latin 'e' developed into the Spanish diphthong 'ie', a process called diphthongization that occurred in stressed syllables during the development of Spanish from Latin.

While 'siempre' itself is a fundamental Spanish word, it's interesting to note that it stands somewhat alone in modern Spanish, without many common related words sharing the same root. This makes it an essential vocabulary word to learn on its own.

While English doesn't have any common everyday words directly related to 'siempre', you might encounter the Latin 'semper' in formal or academic contexts. It's famously used in mottos like 'Semper Fidelis' ('Always Faithful'), the motto of the United States Marine Corps, and 'Semper Paratus' ('Always Ready'), the motto of the United States Coast Guard. The Latin 'semper' is also used in scientific terminology, particularly in botany where 'sempervivum' refers to plants that are evergreen or long-lived (literally 'always living').