Adjectives with Latin etymology when noun has non-Latin etymology

Solution 1:

Let's not forget that Latin was the language of science and philosophy and nearly all higher learning for hundreds of years. For example, Copernicus wrote his seminal treatise about the heliocentric theory, De revolutionibus orbium coelestium, in Latin. It's not surprising that many of the technical names for natural phenomena and educated words in general would be derived from Latin.

We see remnants of this today in medicine: the parts of the body are named from the Latin. Your orthopedist will tell you you've torn your medial collateral ligament in your knee.

Solution 2:

The sort of vocabulary that you would expect the simple folk of the Dark Ages to be using are mostly still of Germanic origin; they are the building blocks of the language, the basics of verb and noun forms, and words for basic abstract concepts.

In later years, the Catholic Church's supremacy meant that the language of inquiry, knowledge, and spirituality was Latin. For many centuries, scientists would publish all their work in Latin. It is no surprise that Latin has filled the gaps in English and provided adjectives such as lunar where English had none.

This is compounded by the imposition of Norman French in the Middle Ages. Since the language of government changed from English, many of our words for government and justice derive from Latin via Norman French. Our words for meats also come from Norman French, e.g. beef, veal, venison, mutton in place of English cow, calf, deer, sheep.

Later still, British scholars would turn to Latin and Greek to coin new words to describe new technologies and modern concepts, as we still do today.

There's an interesting discussion of the influence of Latin on English on wikipedia here: http://en.wikipedia.org/wiki/Latin_influence_in_English

Solution 3:

The English language is a hotchpotch of many languages, a melting pot from most European language roots, with a good deal of other elements thrown in for added spice.

As a result, we often have a vast array of words to choose from for any given topic of conversation. The more elemental and eternal the concept, the longer we will have talked about it and thus the further back through our history words will have been borrowed in order to discuss the concepts.

Generally, you will find that the simple forms of words are likely to hark back to older influences; basic words are often from Old English, or Saxon influence. Whilst more technical terms may not have been so common in the vernacular speech, so may retain scientific form, coming from Latin or Greek.

The essential rule to remember is that English etymology is a many splendored thing; variety is the spice of life, after all.

Solution 4:

Some [simplistic] reasons:

The Latin-based adjective is more elegant for contextual reasons, e.g. sideways vs. lateral
It is impossible to form an adjective otherwise, e.g. sun :: solar
And better a word than a phrase, e.g. lunar vs. of the moon
The non-Latin adjective may mean something else entirely, e.g. handy vs. manual

Solution 5:

To emphasize Robusto's point (3). Sir Issac Newton published his Philosophie Naturalis Principia Mathematica not in English but in Latin in 1687. This was the last major work written in Latin published in England. However, the level of Latin at Cambridge and Oxford was and remained quite high.
Perhaps no more than that of Gottingen or Tubingen in Germany. But "OxBridge" exerted more influence on the Kingdom of England than Gottingen/Tubingen et al exerted on the many German States.
To the English writer back then (and even till the present) Latin roots seem more fitting for abstract words.