The definition for 'extensible' at m-w.com reads 'capable of being extended'. So what's 'extendable' useful for? - it says it means 'to stretch'. I was surprised recently to find that XML is 'extensible markup language', not 'extendable' as I previously thought. 'Extensible' seems therefore to mean something that can be added to like XML, whereas 'extendable' would apply to something more like a telescopic lens, but there doesn't seem to be a very solid convention here - or is there? Which do you guys favour and for which usages?

I've got to recuse myself, never having heard the word extensible used in the wild.

During Strength of Materials class, when I was at the other end of my career, we were taught that theoretically there was no such thing as a non-extensible material; such a material would be so brittle that it would snap as soon as a tensile force was applied to it - like a very short pastry.

But in general use, as you say, the distinction is far from clear. Extensible seems to me to indicate stretchability whereas extendable suggests an opening out or lengthening. An elastic band is extensible, ie: it can be stretched, whereas my lunch hour is extendable, ie: it can be added to, but an hour is an hour and cannot be stretched. That may be a purely engineering view of it though, we do value our lunch hour.

There is also extensile which seems to mean the same as extensible.

> An elastic band is extensible, ie: it can be stretched, whereas my lunch hour is extendable, ie: it can be added to, but an hour is an hour and cannot be stretched.

That makes plenty of sense, but it seems some think that exactly the opposite should be the case. I think if I have to settle one way or the other I'll opt for your definitions, dxb.

> There is also extensile which seems to mean the same as extensible.

Don't go extensiling things.

In reply to:

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we were taught that theoretically there was no such thing as a non-extensible material

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How about something like mica?

[Thanks for these fine distinctions, dxb]

Don't go extensiling things.
Interestingly enough, OED has "extendable, obs. form of extendible." This shows once more the extensible nature of Latin.

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.

'Extensible' seems therefore to mean something that can be added to like XML, whereas 'extendable' would apply to something more like a telescopic lens, but there doesn't seem to be a very solid convention here


I was thinking that things that have extension along one dimension are extendable, whereas things that might be extended along numerous dimensions are extensible. Don't know that it's true, but it's what I always assumed.

k

I would agree with dxb's version Extensible seems to me to indicate stretchability whereas extendable suggests an opening out or lengthening.


Whereas extensiling is painting out the trompe l'oeille trellis you were so proud of during your Martha Stewart phase.

And then there's 'distensible':


"adjective: capable of being distended; able to stretch and expand "

And 'tensible':

(a.) Capable of being extended or drawn out; ductile; tensible.

If dxb is correct in his reasoning (which seems logical), it sounds like the further v. farther debate to me:

Farther is used when describing distance (as in far, farther), and
Further is used when describing time.

Likewise it would seem extensible deals with something tangible and extendable does not (in its true meaning anyway; I've heard things like "extendable umbrella" and whatnot quite often).