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              pinnacle
Here are 3 definitions from The American Heritage Dictionary - it's nr 3 that you'll need most often in general and business communication
1. Architecture. A small turret or spire on a roof or buttress. 
2. A tall pointed formation, such as a mountain peak. 
3. The highest point; the culmination. 
Synonyms:
apex, apogee, ascendancy, climax, crest, crowning point, culmination, cusp, extremity, head, height, high spot, highlight, intensification, limit, maximum, meridian, pay-off, peak, pinnacle, summit, top, turning point, utmost, vertex, zenith
From Late Latin pinnaculum, diminutive of Latin pinna, feather.