Mereology: logical study of the relation between parts and wholes (in philosophy and mathematics). Meromorphic function: like a holomorphic function but only partially defined (in Calculus with complex numbers). Contrast όλος (ancient ὅλος, where the extra symbol indicated an h sound), meaning whole.
:-) Well, yes it is sometimes colloquially to avoid saying "delicate subjects" like toilet much as we say WC in other parts of the world, in the US Rest Room is used in some places. So, in Greece, we can say "the place" or το μέρος and of course people know you're referring to the toilet. Now, I think it's not uncommon to just say: "που είναι η τουαλέτα; παρακαλώ." Hope that helps.
"το μέρος" is very colloquial. It can be used among friends but when asking unknown people you should say "πού είναι η τουαλέτα, παρακαλώ;" And in very formal speech you should say "αποχωρητήριο". There are also some less used synonyms like "απόπατος" and "αφοδευτήριο" :))
η pronounced like a ι (iota). For distinctions, see Horrocks, Greek: A History of the Language and its Speakers, xviii-xix (alphabet), ch. 6 ("Spoken Greek in the Roman Empire"), ch. 11 ("Spoken Greek in the Byzantine Empire: The Principal Developments"). Exactly when η was pronounced / i / is not certain but sporadic evidence indicates at least as early as 2nd century CE (Gignac, Grammar of Gk Papyri: Phonology, 1.274). We don't always know how ancient Greek was pronounced, but if you read Horrocks and Gignac you will be as informed as most.