Here is an unusual spelling: rere for rear. The word probably derives from the Old French rere, rier, from Latin retro (back, behind). The Oxford English Dictionary describes rere as obsolete except in combinations, but this is untrue: it’s a standard variant form in Hiberno-English and is not uncommon on the island, especially in architectural, geographical, and property-related contexts:
to the rere of dwellings on the north side of Rochestown Road (Irish Statute Book)
an old jaunting car proceeding at a slow pace at the rere of the hearse (Offaly Historical & Archaeological Society)
the raised courtyard to the rere of the Irish Film Centre (Archiseek)
At the rere was a massive stone wall (Galway Advertiser, 1883)
they received an allowance of bread or a biscuit, and were dismissed by another door in the rere of the building (The History of the Great Irish Famine of 1847)
There is rere service access. (MyHome.ie)
he keeps his ware house at the rere of his late dwelling-house (Kilkenny Archaeological Society)
return to the hill at the rere of the house (“The Poteen”, from the Dublin Penny Journal, 1832)
This small selection disproves the OED‘s assessment. Many more examples are to be found in both historical and contemporary texts.
Two related notes:
(1) The idiom in the post title, rear its head, is a vivid phrase meaning appear, and is often used to refer to something unpleasant, especially in the form rear its ugly head. The simple form first reared its head around the time of Milton; rear its ugly head came later.
(2) If you happen to be reading this over a midnight feast — rare meat and eggs, perhaps — you could name your meal a rere-supper, a now-archaic term for a (usually sumptuous) late supper. I should warn you, though, that this practice is inadvisable not just for mogwai but for people too: beware of rere sopers!
Edit: On Twitter, @psneeze tells me he was “taught to use it in primary school (late 70s) to distinguish it from rear as in to rear children” [italics added].