Learn how to say Diagonalisable correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word diagonal:
(of a straight line) joining two opposite corners of a square, rectangle, or other straight-sided shape.
(of a line) straight and at an angle; slanting:
a tie with diagonal stripes
a straight line joining two opposite corners of a square, rectangle, or other straight-sided shape.
Mathematics the set of elements of a matrix that lie on a line joining two opposite corners.
a slanting straight line:
the bars of light made diagonals across the entrance
tiles can be laid on the diagonal
Chess a slanting row of squares whose colour is the same.
mid 16th century: from Latin diagonalis, from Greek diagōnios ‘from angle to angle’, from dia ‘through’ + gōnia ‘angle’