'low-hydrogen' is a modern English compound formed from 'low' + 'hydrogen'. 'low' ultimately comes from Old English (e.g. forms in Old/Middle English) meaning 'not high' or 'below', while 'hydrogen' entered English via French 'hydrogène', coined from Greek elements 'hydro-' meaning 'water' and '-genes' meaning 'producer/former'.

'hydrogen' developed from Greek 'hydro-' + '-genes' into French 'hydrogène' and then into modern English 'hydrogen'. 'low' existed in Old and Middle English with a basic sense of 'not high'; the specific compound 'low-hydrogen' arose in modern scientific/technical English to describe materials or environments with reduced hydrogen content.

The component words kept their general senses ('low' = not high; 'hydrogen' = the chemical element named from Greek for 'water producer'), and the compound came to mean 'having a lower-than-normal hydrogen content' in technical usage.