There are ways in Latin of expressing less-than-completeness, but I'm intrigued by the strange-ish (!) and allegedly related etymologies given in English dictionaries for these two endings, which are claimed to be derived from Latin and earlier sources.
I recently came upon the phrase 'a goodish way', for which I used the comparative longius, in the (alternative) sense of 'rather' or 'somewhat'. Almost immediately afterwards the word 'yellowish' occurred, and for this there is an adjective fulvaster. And today I have come upon novellaster, 'newish' or 'rather new'.
This has all set me reflecting that -ish is a useful modifier for English adjectives, and that in French -âtre has a similar use in, for example, verdâtre, 'greenish' (though I do not think it so freely used as our English -ish). The -aster ending is seen in the English 'poetaster' in the same sense while, Chambers' Dictionary attributes the same ending in 'disaster' (via French) to — I quote — [O Fr . . . . from des (L dis-) with evil sense, and astre a star, destiny, from L astrum, Gr astron star].
Although I've found the above examples, I don't remember any rule for modifying Latin nouns and adjectives in analogous ways — except that, in some cases, the prefix sub- can be used as in, for instance, subruber and subraucus. The whole business seems quite haphazard. It would be very convenient if there were a proper rule: is there any such?