A sentence which contains only one main clause. Examples are: She is coming; The king is dead; My brother wants to buy a new car.
The simplest form of an English noun. This is the form which is entered in a dictionary. Examples are: dog, tree, girl, flower etc. A countable noun has two forms: a singular form and a plural form. With an uncountable noun, the singular is the only form that exists at all.
A particular English construction in which an adverb splits an infinitive and its marker to. Examples are:
She decided to never call him again. Here the sequence to never call is an example of what is called a ‘split infinitive’.
Those who use the term split infinitive believe that there is something wrong with separating the particle to from a following infinitive. They are of the opinion that to is itself part of the infinitive and they object to breaking up the sequence. But this view is quite wrong because the infinitive is a single word and the particle to is not part of the infinitive at all.