The rule is for French adjectives that end with -if at the masculine to end with -ive at the feminine, e.g..
actif / active
affirmatif / affirmative
aggressif / aggressive
décisif / décisive
…
On the other hand, nouns in -if/-ive, often substantivated adjectives, generally exists with a single gender and their ending match it, e.g.:
Un adjectif
Un adhésif
Un apéritif
Un canif1
Un explosif
Un motif1
Un récif1
…
Une archive1
Une coopérative
Une directive
Une incisive
Une initiative1
Une lessive1
Une locomotive1
Une perspective
Une rétrospective
Some nouns (referring to persons) exist with both genders:
Un sportif/une sportive
Un fugitif/une fugitive
Un juif/une juive
There is also un esquif/une esquive where the nouns have an unrelated etymology and different meanings.
Finally, there are very few gender/ending mismatches:
Un convive1
Un détective1
Une manif1 (here just because it is a short form of une manifestation)
Détective is likely masculine simply because it was borrowed “as is” from English and there was only male detective at that time. Nowadays, it is definitely possible to say une détective when talking about a woman.
1Nouns not derived from an adjective.
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