IPA: /ˈmaʊn.tɪn.tɑp/
KK: /maʊntɪnˌtɑp/
The highest point of a mountain.
We reached the mountaintop just in time to see the sunrise.
Mountaintop → It is formed from "mountain" (from Old French *montaine*, meaning a large natural elevation of the earth's surface) and "top" (from Old English *top*, meaning the highest point). The word "mountaintop" refers to the highest point of a mountain.
Imagine standing at the "highest point" ('top') of a "large elevation" ('mountain') — that's what a mountaintop is.
No commonly confused words.