1.
third floor
The third story of a multi-story building. Note that in Japan (as in most of Asia), the first floor (一階) is the ground floor, so 三階 corresponds to what would be the 'second floor' in British English.
三 (three) + 階 (floor, story). The reading of 階 undergoes rendaku to がい after 三.
Pronunciation
Both さんがい and さんかい are heard, but さんがい is the traditional and more common reading. The non-rendaku さんかい is increasingly used by younger speakers, especially because the homophone 三回 (three times) is read with the same さんかい — this can cause confusion in speech.
Common collocations
Counting floors
Related Words
Related:
何階 (what floor)