What does "iff" mean?

Initialism of identification friend or foe.

What is a synonym for "iff"?

Common synonyms include: identification friend or foe, identification friend or foe.

Pronounced //ɪf ən(d)ˈoʊn.li ɪf//.

//ɪf ən(d)ˈoʊn.li ɪf// conj, name, noun

conj, name, noun ·Rare ·Advanced level

Noun

1
Initialism of identification friend or foe. abbreviation, alt-of, initialism
"Another red alert last night. Lasted only five minutes, Possibly just a friendly plane with its IFF turned off."

Conjunction

1
Abbreviation of if and only if. abbreviation, alt-of
"A rectangle is a square iff all four of its sides have the same length."
2
Obsolete spelling of if. alt-of, obsolete
"For iff the patient be aſhamed to diſcloſe hiſ wounde to the phyſician which knoweth it not , phyſicke can not helpe him."

Proper Noun

1
Initialism of Interchange File Format, a file format standard developed for Amiga computers. abbreviation, alt-of, initialism
2
Initialism of International Flavors & Fragrances abbreviation, alt-of, initialism

"An integer is natural iff it is greater than or equal to 0."

Data sourced from Wiktionary, WordNet, CMU, and other open linguistic databases. Updated March 2026.