"dual forms" is a correct and usable phrase in written English.
It can be used to refer to two different varieties that have similar features. For example, "This language has both singular and dual forms to denote plurality."
There were separate dual forms for pronouns only.
In dual forms, the verb is also gendered, e.g. katabā (two men wrote) versus katabatā (two women wrote).
In the Square Hebrew alphabet there are five letters kaf, mem, nun, pe, and tzade that have dual forms.
In Germanic these were reduced to indicative, imperative, and subjunctive moods; a full active voice plus passive found only in Gothic; three persons; full singular and plural forms and dual forms found only in Gothic; and one infinitive (present) and two participles (present and past).
The pronouns of the 1st and 2nd persons still had distinctive dual forms: There were two demonstratives: sē, sēo, thaet, meaning "that," and thes, thēos, this, meaning "this," but no articles, the definite article being expressed by use of the demonstrative for "that" or not expressed at all.
Some equivalent forms, the dual forms as well as some related homogeneous cases, are also considered.
Others count differently – they may have a plural form meaning "of unexpected number" or a dual form.
The dual form found special favour in Cambodia, where inscriptions and images from the 6th 7th century are known.
I recommend dual form NRT because there is very strong evidence that this gives better results than using one form of NRT by itself.
Dual form means a transdermal patch plus one of the other products such as gum, lozenge, nasal spray, mouth spray or inhalator.
This may in turn be formulated in a dual form.
