The Collaborative International Dictionary of English v.0.48:

Noontide \Noon"tide`\, n. [From noon + tide time; cf. AS.
   n[=o]nt[imac]d the ninth hour.]
   The time of noon; midday.
   [1913 Webster]

WordNet (r) 3.0 (2006):

noontide
    n 1: the middle of the day [syn: noon, twelve noon, high
         noon, midday, noonday, noontide]