Adaptive describes the ability to adjust to new conditions, as in an adaptive interface that rearranges itself. Adoptive describes family relationships formed by adoption rather than birth, as in her adoptive parents. Link adoptive to "adopt" and family; link adaptive to "adapt" and change.
The core difference
Adaptive is about adjusting to change; adoptive is about family ties formed through adoption.
- adaptive — able to adjust or change in response to new conditions: Adaptive behavior helped the species survive a changing climate.
- adoptive — related by adoption rather than by birth: He stayed close to his adoptive family throughout his life.
How to tell them apart
Both words end in -ive, but they come from different verbs. Adaptive comes from adapt, meaning to adjust to new conditions, so it describes anything that changes or responds flexibly, from technology to living creatures. Adoptive comes from adopt, meaning to take a child into your family, so it always relates to family formed through adoption rather than biology.
Because the two words are only one letter apart, they are easy to mistype in family or biology writing. A safe check: if you mean "changes to fit circumstances," you want adaptive; if you mean "related through adoption," you want adoptive.
