Learn how to say Onto correctly in English with this tutorial pronunciation video.
Oxford dictionary definition of the word onto:
1variant form of on to (see on).
2 Mathematics expressing the relationship of a set to its image under a mapping when every element of the image set has an inverse image in the first set:
an onto mapping
The preposition onto written as one word (instead of on to) is recorded from the early 18th century and has been widely used ever since, but is still not wholly accepted as part of standard British English (unlike into, for example). Many style guides still advise writing it as two words, and that is the practice followed in this dictionary. However, onto is more or less the standard form in US English and in the specialized mathematics sense. Nevertheless, it is important to maintain a distinction between the preposition onto or on to and the use of the adverb on followed by the preposition to:
she climbed on to
let’s go on to
the next point