What caught my eye about
unitize/ise was the two main meanings of the word: "to form or combine into one unit, as by welding parts together", and "to divide or separate into units". In other words, it can mean either to combine or to separate. This seems to qualify it as a
contronym, or
antagonym. As described at
http://www.rinkworks.com/words/contronyms.shtml, these rare specimens are words like
cleave (= separate, or adhere), that have meanings more or less opposite to one another.
The word
unitizer is generally used for various types of machine, although it has also been used in writings about language structures. A broader use was in an 1864 article in the
Continental Monthly: "Wagon roads, canals, railroads, telegraphs, are all so many political unitizers; but the railroad, with its accompaniment, the telegraph, may be regarded as the chief of all." (It seems that the meaning intended here could probably have been conveyed just as well by
unifiers.) The spelling
unitiser does appear - it's rare, but so is
unitizer. I think the argument from consistency should prevail in this case, so I will admit
unitiser to our list.
On the general question of
-ize and
-ise endings, it's true that
-ize was once the standard for all English-speakers. British usage has been migrating to
-ise for some time, but
-ize is still favoured by some British writers and publishers. The issue was discussed a few years ago by Michael Quinion on his
World Wide Words website. I think the trend to
-ise has gone further here in Australia than in the UK, and the
-ize forms are seldom seen in texts originating from here. Even the Oxford, in its Australian and New Zealand dictionaries, gives the
-ise spelling first.