'rock-like' is formed by combining the noun 'rock' and the adjective-forming suffix '-like' (from Old English 'līc' meaning 'body, form, likeness').

'rock' originates from Old English 'rocc' (of Germanic origin, exact earlier source uncertain). The suffix '-like' comes from Old English 'līc' which produced adjectival forms meaning 'having the form of' and later the productive suffix '-like'. These elements combined in Modern English to form compounds such as 'rock-like'.

Originally, Old English 'līc' meant 'body' or 'form'; over time it evolved into the suffix '-like' meaning 'similar to' or 'having the characteristics of', so 'rock-like' now means 'similar to rock'.