impersonal pronoun 
noun
The pronoun it when used without definite reference or antecedent, as in it was snowing and it seems hard to believe.
- infrangibility
- infrangible
- infrangibly
- infraorder
- infrared
- infrared sensor
- infrarenal
- infrasonic
- infrasound
- infraspecific
- infrastructural
- infrastructure
- infrequency
- infrequent
- infrequently
- infringe
- infringement
- infringer
- in front
- in front of
- (at) full pelt
- at (full) strain
- at full stretch
- (at) full tilt
- at grade