'rockiness' is formed in Modern English by adding the noun-forming suffix '-ness' to the adjective 'rocky'. The adjective 'rocky' comes from the base noun 'rock'. 'Rock' originates from Old English 'rocc', meaning 'stone' or 'large stone'.

The element 'rock' comes from Old English 'rocc' (meaning 'stone'); from that developed the adjective 'rocky' (Old English/Middle English development), and in Modern English the suffix '-ness' (from Old English '-nes(s)e') was attached to form 'rockiness'.

Originally referring primarily to the physical presence of rocks ('full of stones'), the word's usage expanded to include figurative senses of instability or difficulty (e.g., the 'rockiness' of a relationship).