Sexual (n.) is not the same as genital — the confusion of the two is why doctors refuse to see thumbsucking as sexual.
The Sexual (n.) need not be genital, just as the psychical need not be conscious: psychoanalysis widened both concepts the same way.
The Sexual (n.) is first of all the improper, the thing one must not talk about — so that a famous psychiatrist could say "there's nothing sexual about childbirth."
Sexual (n.) defeats every attempt at definition: centre it on reproduction and kissing falls out; centre it on the opposite sex and childbirth does.
The Sexual (n.) is thus what is accomplished through the genitals, but which is already there in 'the localized pleasure of the organs'. In more scientific terms, it is the application of a biogenetic principle, according to which the product of a process of development derives, in its mode of existence, from the existence of the process itself.