- flat-coated retriever
- flat-earther
- flatfeet
- flat-file database
- flatfish
- flatfoot
- flat-footed
- flatfoots
- flat-hat
- Flathead
- flathead cat
- flathead catfish
- Flathead River
- Flathead Valley Community College
- flatiron
- flatland
- flatlet
- flatlets
- flatling
- flatlings
- flatlins
- flat out
- flat-out
- flat oyster
- flat-panel display