Meaning of -ATIVE in English
-ative BrE AmE ət ɪv, eɪt ɪv AmE ət̬ ɪv, eɪt̬ ɪv In words of three syllables, the first receives the stress, and the suffix vowel is weak ( ˈ fricative, ˈ vocative, ˈ laxative, ˈ narrative; exception cre ˈ ative). In longer words, the stress usually falls on the same syllable as in the underlying stem: ac ˈ cusative, con ˈ sultative, pre ˈ servative; ˈ operative, ˈ qualitative, ag ˈ glutinative, ˌ argu ˈ mentative; ad ˈ ministrative. There is sometimes a vowel change (de ˈ rive — de ˈ rivative), and there are several exceptional cases (com ˈ bine — ˈ combinative, ˈ alternate — al ˈ ternative, in ˈ terrogate — ˌ inter ˈ rogative, ˈ demonstrate — de ˈ monstrative). Where the primary stress is on the last syllable of the stem, the suffix has a reduced vowel ( ˌ inter ˈ rogative); but otherwise in these longer words ( ˈ cumulative, ˈ legislative) the choice between weak-vowelled ət ɪv AmE ət̬ ɪv and strong-vowelled eɪt ɪv AmE \ eɪt̬ ɪv depends partly on social or regional factors, with British English RP tending to prefer ət ɪv , American English eɪt̬ ɪv : see individual entries.
Longman Pronunciation English Dictionary. Английский словарь произношений Longman. 2012