the British Isles have got the most confusing nomenclature around. There are at least 15 names of major overlapping political and geographical entities here, ignoring all the counties and bailiwicks and islands and the like. But the real problem is the endemic shortage of adjectives. Of the 15 names, 8 have no adjectival form, as far as I can tell. One (Scotland) has three different adjectival forms: Scots for the language and (mostly) the people; Scotch for the local distilled liquor; Scottish for everything else, more or less. There are four other (ambiguous) adjectives, all irregular formations with -ish or similar endings: British, English, Irish, Welsh. But the large-scale formal political entities centered in London -- United Kingdom, Great Britain -- are entirely bereft of corresponding adjectives, except for the jokey UKish and the irregular, ambiguous and confusing pair British and Britannic.
There's a table there, to illustrate just how ridiculous our adjective shortage is here. Nothing there that the residents of these islands don't already know, but we just don't usually think about it. It's quite a shock to see it all laid out.