Examples of synonyms starting with letter I?

Answer 1

Similes are comparisons. There is not some giant list of "All Similes Known To Man" that you can look at to see what letter they start with. You simply compare two things and say "This is as ___ as ___"

Answer 2

What word do you need a synonym of? Synonym means 'word of same meaning', so you need to specify the original word before anyone can think of a synonym beginning with 'I'.