meridian in WordNet English dictionary

1. the highest level or degree attainable; the highest stage of development
   "his landscapes were deemed the acme of beauty"; "the artist's gifts are at their acme"; "at the height of her career"; "the peak of perfection"; "summer was at its peak"; "...catapulted Einstein to the pinnacle of fame"; "the summit of his ambition"; "so many highest superlatives achieved by man"; "at the top of his profession"
   acme  height  elevation  peak  pinnacle  summit  superlative  meridian  tiptop  top 
   
2. an imaginary great circle on the surface of the earth passing through the north and south poles at right angles to the equator
   "all points on the same meridian have the same longitude"
   meridian  line of longitude 
   

1. of or happening at noon
   "meridian hour"
   meridian 
   
2. being at the best stage of development
   "our manhood's prime vigor"- Robert Browning
   prime  meridian