Usage tip: extended vs. extensive and the like

Thanks to reader and English teacher Ryan for this topic suggestion. It's a good one!

All adjectives are not equal. Well, you knew that already. But sometimes two adjectives appear to be interchangeable because they have the same root and have endings that clearly indicate they are both adjectives--yet they have two different correct usages. The -ed and -ive endings sometimes create this kind of look-alike confusion. Here are three examples of fine shades of difference between similar words. (Note: In all three cases, the -ed word can also be used as a verb, but those usages don't give most English users as much trouble. Therefore, I've only dealt below with the more commonly confused adjective usages.)

extended/extensive

extended: having been made longer or broader
extensive: thorough

Ex: Originally scheduled for two hours, the Wilderness Explorers' extended examination of the marsh stretched to a full day. Their extensive observation revealed half a dozen potentially new or unrecognized species.

exhausted/exhaustive

exhausted: extremely fatigued
exhaustive: absolute; complete

Ex: Already exhausted by the long international flight, we were physically unprepared upon landing to conduct an exhaustive search for our missing luggage.

adopted/adoptive*

adopted: having been legally accepted into a family other than the one to which one was born
adoptive: having legally accepted someone into one's family

Ex: The adopted child was four months old when his birth parents gave him up; his adoptive parents are the only ones he has ever known.

*Note that in many cases adopted is considered acceptable for both halves of the relationship, but adoptive is traditionally applied only to the guardian, not the child.

Certainly there are other examples of this type. Readers, use the comments section to add to the list, share hints or tips for remembering the differences, or ask questions. I look forward to your input!