A correspondent writes to ask if there are any rules governing the use of -ish in English. He says ‘we tend to add it to short adjectives, particularly colours and physical attributes: shortish, tallish, greenish... but googling reveals that we add -ish to just about every adjective under the sun, such as beautifulish, Europeanish, freezingish, exhaustedish...’
He’s right to draw attention to the monosyllabic character of the adjectives. This is an important factor when it comes to inflections in English. We see it in the comparative and superlative forms too, where the distribution of -er and -est vs more and most correlates strongly with length. We prefer bigger to more big. Adjectives with three syllables or more use the other construction (more interesting, not interestinger). There are just a few exceptions, such as unhappier. Adjectives with two syllables are more difficult to describe: some take the inflection (eg those ending in -y and w, such as happier, narrower), some don’t (eg those ending in -ed, such as more worried), and some take both (eg commonest and most common).
A similar situation applies in the case of -ish. In the sense of ‘somewhat’, we find it added to monosyllabic adjectives from Middle English times - colour words such as bluish (1398) and blackish (1486) are among the earliest. Adjectives ending in y and w attract it too: sillyish (1766), narrowish (1823). The usage then extended to other monosyllabic adjectives, such as brightish (1584), coldish (1589), and goodish (1756), and the usage has continued to extend over the centuries. In the early 20th century we find it used for hours of the day or number of years, probably motivated by earlyish and latish - ‘See you at about eightish’, ‘She’s thirty-ish’. Note elevenish, forty-five-ish, 1932-ish, and so on, where the root has three or more syllables.
This ties in with a second use of -ish, where it’s added to nouns in the sense of ‘having the character of'. Some, such as childish and churlish, and the nationhood names such as English and Scottish, go back to Old English. Among later arrivals are boyish (1542) and waggish (1600) - the latter a first recorded use in Shakespeare, as is foppish and unbookish. (Shakespeare quite liked the suffix - knavish, dwarfish, thievish, hellish, etc.) Note that most have a derogatory sense. Again, most are monosyllabic, but we do find the occasional longer form, such as babyish, womanish, and outlandish. This trend really took off in the 19th century, when novelists and journalists extended it to proper names. We find Micawberish, Queen Annish, Mark Twainish, and suchlike, as well as some colloquial phrases - ‘You look very out-of-townish’, ‘He has a how-do-you-do-ish manner’.
What we’re seeing today - and what my correspondent has noted - is the further extension of these patterns in informal contexts to longer adjectives. I can’t see any restriction here, other than the stylistic one - they are informal, colloquial, jocular, daring. There’s a youtube site called extraordinaryish. But one senses the novelty - as does Google. When I typed it in, to see if it was used (I got 193 hits), it was worried. ‘Did you mean extraordinary fish’, it asked.