'hornblende-poor' is a modern English compound formed from 'hornblende' + 'poor'. 'Hornblende' was adopted into English from German 'Hornblende' (German 'Horn' + 'Blende'), where 'Horn' means 'horn' and 'Blende' referred to a deceptive-looking mineral; 'poor' comes from Old French 'povre' ultimately from Latin 'pauper' meaning 'impoverished' or 'lacking'.

'Hornblende' entered geological English from German in the 18th–19th centuries to name a dark amphibole mineral; 'poor' has been used in English since Old French/Latin times to mean 'lacking'. The compound 'X-poor' arose in modern scientific/technical English to describe rocks or materials having little of component X, hence 'hornblende-poor' in geological descriptions.

Individually, 'hornblende' designated a specific mineral and 'poor' meant 'lacking'; combined in geological usage they specifically denote 'lacking hornblende' in a rock or sample — a descriptive, literal compound whose meaning has remained direct and technical.