Origins
The Latin word 'stēlla' — meaning 'star' — is one of the oldest and most transparent inheritances from Proto-Indo-European. The PIE root *h₂stḗr (star) is among the most securely reconstructed words in comparative linguistics, with reflexes in virtually every branch of the family, and its meaning has remained essentially unchanged for over six thousand years.
The reconstruction *h₂stḗr is supported by an unusually consistent set of cognates. Greek gives ἀστήρ (astḗr) and ἄστρον (ástron). Sanskrit gives stṛ́ and the derivative tā́rā (star). Avestan gives star-. Armenian gives astł. Gothic gives stairnō. Old English gives steorra (Modern English 'star'). Old High German gives sterno (Modern German Stern). Old Irish gives ser. Hittite gives ḫasterz. The agreement is so regular that *h₂stḗr serves as a textbook example in introductory courses on historical linguistics.
The Latin form stēlla developed from an earlier *stērelā (or *sterela) through a regular process of assimilation: the r and l in close proximity resolved to ll. This change distinguishes the Latin form from its Greek and Germanic cousins and gives the Latin-derived English words their characteristic -ll- spelling: stellar, constellation, stellate.
Latin Roots
In Classical Latin, stēlla meant a star or heavenly body of any kind, including planets (which the Romans called 'stēllae errāticae,' wandering stars). The diminutive form stēllula appears in poetry. The derived verb stēllāre meant 'to set with stars' or 'to cover with starlike points.' The compound cōnstēllātiō (from con- 'together' + stēlla) meant 'a set of stars' — a group of stars considered as a figure or pattern.
English borrowed from Latin stēlla through two channels. The learned, direct borrowings arrived during the Renaissance and later: 'stellar' (1656, from Latin stēllāris, 'of the stars'), 'interstellar' (1626, coined in English from inter- + stellar), 'stellate' (star-shaped, from Latin stēllātus), and 'stellify' (to transform into a star, from Late Latin stēllificāre). These remain relatively technical or literary words.
The more common borrowing, 'constellation,' arrived much earlier through Old French. Latin cōnstēllātiō entered Old French as constellation and was borrowed into Middle English around 1340. Originally it referred to the position and grouping of heavenly bodies, especially as believed to influence human affairs (the astrological sense). The astronomical sense — a recognized pattern of stars — became dominant as astrology and astronomy diverged.
Greek Origins
The parallel Greek branch, from ἀστήρ, contributed a far larger vocabulary to English, though by a different route. 'Astronomy' (from ἄστρον + νόμος, 'star-law'), 'astrology' (from ἄστρον + λόγος, 'star-study'), 'asteroid' (from ἀστεροειδής, 'star-like'), 'asterisk' (from ἀστερίσκος, 'little star'), and 'astronaut' (from ἄστρον + ναύτης, 'star-sailor') all descend from the Greek cognate. Even 'disaster' belongs here: from Italian disastro, from dis- + astro ('ill-starred'), reflecting the ancient belief that unfavorable stellar configurations brought misfortune.
The native English word 'star' descends from the same PIE root through the Germanic branch: PIE *h₂stḗr > Proto-Germanic *sternǭ > Old English steorra > Middle English sterre > Modern English star. The vowel changes and the loss of the n reflect regular Germanic sound shifts. English thus has three parallel star-word families — Germanic 'star,' Latin 'stellar/constellation,' and Greek 'astro-/aster-' — all from the same six-thousand-year-old root.
As a personal name, Stella has been popular since the Renaissance. Philip Sidney created 'Stella' as a literary name for Penelope Devereux in his sonnet sequence 'Astrophel and Stella' (1591), combining the Greek ἀστήρ (star-lover) with the Latin stēlla (star). The name became widely popular in the English-speaking world and remains so today, a living reminder that the Latin word for star has never left common use.
Proto-Indo-European Roots
The persistence of *h₂stḗr across time and space illustrates a general principle: words for the most visible, universal features of the natural world — sun, moon, star, water, fire — tend to be among the most conservative elements in any language, resisting replacement and changing slowly. The night sky is the same sky the Proto-Indo-Europeans saw, and the word they used to name its brightest points has survived, in recognizable form, for over six millennia.