'semi-mobile' originates from the Latin prefix 'semi-' (from Latin 'semis') meaning 'half' and from Latin 'mobilis' meaning 'movable', the latter entering English via French 'mobile'.

'semi-' has been used as an English combining form since Middle English from Latin 'semis', and 'mobile' came into English via Old French from Latin 'mobilis'; the compound 'semi-mobile' is a modern English formation combining these elements to mean 'half-movable' or 'partly movable'.

Initially the components implied 'half-movable' in a literal sense; over time the compound came to be used more generally to mean 'partly or only partially able to move' in technical and everyday contexts.