All pronunciations are given strictly phonetically. This only covers races explicitly named in the first nine books, omitting Undersea races not appearing or mentioned in book nine.
Afanc: ah-fank. Plural is “Afanc.”
Annwn: ah-noon. No plural exists.
Bannick: ban-nick. Plural is “Bannicks.”
Barghest: bar-guy-st. Plural is “Barghests.”
Blodynbryd: blow-din-brid. Plural is “Blodynbryds.”
Cait Sidhe: kay-th shee. Plural is “Cait Sidhe.”
Candela: can-dee-la. Plural is “Candela.”
Coblynau: cob-lee-now. Plural is “Coblynau.”
Cu Sidhe: coo shee. Plural is “Cu Sidhe.”
Daoine Sidhe: doon-ya shee. Plural is “Daoine Sidhe,” diminutive is “Daoine.”
Djinn: jin. Plural is “Djinn.”
Dóchas Sidhe: doe-sh-as shee. Plural is “Dóchas Sidhe.”
Ellyllon: el-lee-lawn. Plural is “Ellyllons.”
Gean-Cannah: gee-ann can-na. Plural is “Gean-Cannah.”
Glastig: glass-tig. Plural is “Glastigs.”
Gwragen: guh-war-a-gen. Plural is “Gwragen.”
Hamadryad: ha-ma-dry-add. Plural is “Hamadryads.”
Hippocampus: hip-po-cam-pus. Plural is “Hippocampi.”
Kelpie: kel-pee. Plural is “Kelpies.”
Kitsune: kit-soo-nay. Plural is “Kitsune.”
Lamia: lay-me-a. Plural is “Lamia.”
The Luidaeg: the lou-sha-k. No plural exists.
Manticore: man-tee-core. Plural is “Manticores.”
Mauthe Doog: mwa-th doo-g. Plural is “Mauthe Doog.”
Naiad: nigh-add. Plural is “Naiads.”
Nixie: nix-ee. Plural is “Nixen.”
Peri: pear-ee. Plural is “Peri.”
Piskie: piss-key. Plural is “Piskies.”
Puca: puh-ca. Plural is “Pucas.”
Roane: row-n. Plural is “Roane.”
Satyr: say-tur. Plural is “Satyrs.”
Selkie: sell-key. Plural is “Selkies.”
Shyi Shuai: shh-yee shh-why. Plural is “Shyi Shuai.”
Silene: sigh-lean. Plural is “Silene.”
Tuatha de Dannan: tootha day danan. Plural is “Tuatha de Dannan,” diminutive is “Tuatha.”
Tylwyth Teg: till-with teeg. Plural is “Tylwyth Teg,” diminutive is “Tylwyth.”
Urisk: you-risk. Plural is “Urisk.”