- protocols
- protocontinent
- protoctist
- protoderm
- protoderms
- protogalaxy
- Proto-Germanic
- protogynic
- protogynous
- protohistory
- protohuman
- Proto-Indo-European
- protolanguage
- protolithic
- protomartyr
- protomorphic
- proton
- proton
- protonema
- protonemata
- protonotary
- protonotary
- protons
- proton synchrotron
- proto-oncogene