The word ending <ious> is pronounced iəs in many words. Here are some examples:
acrimonious amphibious copious curious delirious devious dubious envious fastidious furious glorious harmonious hilarious insidious previous sanctimonious supercilious
However, in quite a few words the ending is əs rather than iəs. This is true of all the words below.
If the preceding letter is <t>, this is pronounced ʃ. Again some examples:
ambitious cautious conscientious contentious fictitious flirtatious ostentatious pretentious propitious vexatious
A preceding <c> or <sc> is also pronounced ʃ, as in:
atrocious capacious conscious delicious ferocious gracious luscious malicious precious precocious spacious tenacious
There are a few words where the preceding letter is <g>. This is pronounced dʒ.
contagious prestigious religious
anxious = ˈæŋkʃəs or ˈæŋʃəs
noxious = ˈnɒkʃəs
obnoxious = əbˈnɒkʃəs or ɒbˈnɒkʃəs
Notice that the main stress of the word falls on the syllable immediately before the ending in all the examples on this page.