This one is as defunct a word as you are likely to meet in this section — it seems to have utterly disappeared from the English lexicon. Like its close relative cancroid, it derives from Latin cancrinus, relating to a crab.
It has been used on rare occasions to mean crab-like but more usually a specialised type of backwards motion, curious in view of its derivation, which would imply a sideways movement to match that of the crab. In this sense, cancrine refers to a type of Latin verse that reads the same backwards as forwards, which we would now refer to as palindromic. The example usually quoted is:
Signa te signa. Temere me tangis et angis.
Roma tibi subito motibus ibit amor
each half of which is cancrine (It was supposedly said by the Devil to St Martin, who had changed him into a donkey and ridden him to Rome. In translation: “Cross thyself, you plague and vex me without need. For by my efforts you are about to reach Rome, the object of your travel”.)
Cancrine doesn’t refer only to verse though: Bach’s Crab Canon, which is a musical palindrome, has also been described as cancrine.