What would be the adjectives for nouns like shopkeeper, country, wife, earring, teacher, father — and so on and so forth?
Although this might not count an answer directly concerning your question, I think some nouns perform as adjectives when collocating suitably with a second noun. In this case the first noun is called an attributive noun. The following is the way my Merriam-Webster's Collegiate Dictionary [11th edition] briefly puts it:
[Some nouns are] often used as an adjective equivalent in attributive position before another noun:
1 bottle ... noun, often attrib.
business ... noun, often attrib.
Examples of attributive use of these nouns are bottle opener and business ethics.
Similarly some attributive collocations of the words you mentioned can be:
earning: earning power/capacity
teacher: teacher appraisal
With that said, the following is what I could find from concise oxford dictionary [10th edition]. [to my eye most of them seem rare/odd/awkward like teacherly]
father: fatherly fatherlike, fatherless.
wife: wifeless, wifely.
Note, too, that in some instances the conversion of a noun to an adjective may not use the original noun. For example, needing an adjective for "wife", some would choose to use the word spousal. Similarly, referring to a teacher, one might use the term didactic. If "country" is used to refer to a nation state, the word national might be used; but if it "country" is used to mean "non-urban", the adjective rural might be used.
The bottom line is, a word doesn't necessarily need to be in adjective form to act as an adjective.
[waiting for natives!]
The question is very general so I will provide the general answer. English nouns convert to adjectives in unpredictable ways. Many nouns have convenient adjectives, often with common suffixes like -ly, -ish, -like, or -esque:
- Wife -> Wifely
- Arab -> Arabesque
- Imp -> Impish
- Life -> Lifelike
- Electricity -> Electric
There may be more such suffixes which I am forgetting.
But many nouns do not have easy translations (Country, for instance). There is a class of colloquial adjectivizations (my own colloquialism) which use the suffixes in the first category when they are not technically allowed –
- Shopkeeper -> Shopkeeperly
- Tony Romo (football player) -> Romo-esque
These hybrids are casual but are fun sometimes to inject a little specific flavor to what you are saying, especially if you want to invoke a proper noun.
Many other nouns have strong adjective relatives which either directly map to the noun or need a little context, but have resemblance to the noun itself:
- Country (if you are talking about regions which are not urban) -> Bucolic, Pastoral, Rural
- Country (if you are talking about nations) -> National, Sovereign
- Train -> Locomotive
- Image -> Visual, Illustrative
- Water -> Aquatic, Moist, Damp
The rest, which often are specific "detail words", have no clear one-word adjective pairing and should be used as part of a metaphor or simile:
- Keyboard -> "The stones were arranged in a loose grid, like a keyboard"
- Ox -> "He is an ox"