Quick answer
Borrowed nouns ending in -о, -е, -и, -у, -ю do not decline at all: в метро́, на метро́, о метро́. Most are neuter.
The common ones
| Word | Meaning | Gender |
|---|---|---|
| метро́ | metro | neuter |
| кафе́ | café | neuter |
| такси́ | taxi | neuter |
| пальто́ | coat | neuter |
| кино́ | cinema | neuter |
| ра́дио | radio | neuter |
| меню́ | menu | neuter |
| ко́фе | coffee | masculine — the exception |
The whole group takes neuter agreement: но́вое кафе́, большо́е метро́, моё пальто́. Ко́фе is traditionally masculine (чёрный ко́фе), though neuter is now tolerated in speech.
People and places
Borrowed personal nouns follow the person’s sex: ста́рый ме́сье, молода́я ле́ди. Foreign place names in -о and -и do not decline either: в Чика́го, в Со́чи, из То́кио — and neither do most foreign surnames ending in a vowel, such as Дюма́ or Ка́мю.
What this buys you
Nothing to memorise and nothing to get wrong: Я е́ду на метро́. Я вы́шел из метро́. Мы говори́м о метро́. One form in every sentence. Learners often decline them anyway out of habit — the only mistake available here is inventing an ending.
The plural too
Indeclinable nouns have no plural ending either. Два кафе́, три такси́, все пальто́ — the number does the work.
Typical mistakes
в метре́
в метро́
The word never changes. Note that метр (a metre) is a different, normal noun.
два такси́х
два такси́
No plural ending exists.
Check yourself
Which is correct?