ul·tra·low frequency 
(ŭl′trə-lō)
(ŭl′trə-lō)n. Abbr. ULF
An electromagnetic wave whose frequency is less than 3,000 hertz.
- investigate
- investigation
- investigational
- investigative
- investigator
- investigatorial
- investigatory
- investiture
- investment
- investment bank
- investor
- inveteracy
- inveterate
- inveterately
- inveterateness
- inviability
- inviable
- invidious
- invidiously
- in view of
- invigorate
- invigoratingly
- invigoration
- invigorator
- invincibility