Compact Oxford English Dictionary
extend
• verb 1 make larger in area. 2 cause to last longer. 3 occupy a specified area or continue for a specified distance. 4 hold out (one’s hand or another part of one’s body) towards someone. 5 offer; make available.

— DERIVATIVES extendability noun extendable adjective extendibility noun extendible adjective extensibility noun extensible adjective.

— ORIGIN Latin extendere ‘stretch out’.

So, this one gives extensibility and extensible as deriviatives (whatever that means) of extend. It has VXML and XML as Results 2 and 3; I was surprised to see that numbers 4 and 5 were chameleon and pelican.
chameleon
/kmeelin/ (also chamaeleon)

• noun a small slow-moving lizard with a long extensible tongue, protruding eyes, and the ability to change colour.

— DERIVATIVES chameleonic adjective.

— ORIGIN Greek khamaileon, from khamai ‘on the ground’ + leon ‘lion’.


pelican

• noun a large waterbird with a long bill and an extensible throat pouch for scooping up fish.

— ORIGIN Greek pelekan, probably from pelekus ‘axe’ (with reference to its bill).
I've included these two usages as a matter of interest, though perhaps not clarity. I wouldn't have used extensible in either of these examples. Maybe because it's a UK site?

Here is the link to the home page:
http://www.askoxford.com/asktheexperts/faq/aboutdictionaries/?view=uk Note: I had difficulty getting it to go back to the previous page. Interestingly, it has no separate def. of extensible; this word's only listings are as above.

Oh, and jfrt: I pronounce chameleon kuh-MEE-uh(l)-yun. Though not with 4 syllables, exactly: mee-ul is more of a dipthong of the ee and the uh vowel sounds--and I hadn't even been aware that I added the uh until I tried writing it out! I first planned to write MEEL as one unit, then realized that wasn't the way I really say it. The uh before the l is definitely there.