As it's St Patrick's Day today, I'll take a look at the word 'shamrock'. The word comes from the Irish Gaelic seamróg, which is a diminutive of the word seamar, the plant 'clover'. The first citation in the OED dates back to 1571. St Patrick supposedly used the shamrock to illustrate the doctrine of the Trinity, which is why it was adopted as the emblem of Ireland.
The OED also has 'to drown the shamrock', which means 'to go drinking on St Patrick's day'. The first recorded mention of that was in 1888, although there is a citation from 1726 which mentions the people 'wetting' their Seamar-oge. The OED also has shamrockshire, described as now obsolete. It dates back to the 1680s and is defined as 'a jocular name for Ireland'.
As I said above, seamróg is a diminutive; -og(e) or -ag(e) are feminine diminutive suffixes in Celtic languages. For instance, the Scottish girl's name Morag is a diminutive of Mor, Sarah. The suffix -ock in English (and similar forms in other Germanic languages) also originally denoted the diminutive (cf hillock). It sounds similar to the Celtic -og, but that's probably just a coincidence.