The i of iti is the single substitute for the at (of a word denoting imitation of an inarticulate sound) + iti,
The sound which is not distinct and clear, is called अव्यक्त; when some one utters distinctly something which has some resemblance to that sound, by some contrivance, it is called अनुकरण् or imitation of that sound. Thus पटत् + इति =पटिति, घटत् + इति = घटिति, झटत् + इति = झटिति, छमत् + इति = छमिति ॥.
Why do we say 'imitation of an inarticulate sound'? Observe जगत् + इति = जगदिति ॥ Why do we say \of अत्\? Observe मरट् + इति = मरडिति ॥ Why do we say when followed by इति? Observe पटत् + अत्र = पटदत्र ॥
Vart:- This applies when the word consists of more than one syllable. Therefore it does not apply in the following:- स्रत् + इति = स्रदिति ॥ How do you explain the form घटदिति in the following:- घटदिति गम्भीरमम्बुदैर्नदितम् ॥ Here the word is not घटत् + इति but घटद् + इति ॥,