infra-infra- /ɪnfrə/ prefix technical 
below something in a range: 
the infra-red end of the spectrum → ultra-(2)
below something in a range: the infra-red end of the spectrum → ultra-(2)- marque
- marquee
- marquess
- marquetry
- Marquette, Jacques
- marquis
- Marrakesh
- marriage
- marriageable
- marriage bureau
- marriage certificate
- marriage guidance
- marriage licence
- marriage lines
- marriage of convenience
- Marriage of Figaro, The
- marriage vow
- married
- Marriner, Sir Neville
- Marriott
- marrow
- marrow bone
- marry
- Mars
- Marseillaise