dvandva

The dvandva is just a collection of words that would otherwise be connected with the word ca (“and”):

• रामो लक्ष्मणश् च → रामलक्ष्मणौ
  rāmo lakṣmaṇaś ca → rāmalakṣmaṇau
  Rama and Lakshmana
  

With the following two rules as context:

• विभाषा। २.१.११
  vibhāṣā (2.1.11)
  vibhāṣā
  Optionally, ...

• अनेकमन्यपदार्थे। २.२.२४
  anekamanyapadārthe (2.2.24)
  anekam anya-pada-arthe
  Many related (padas) denoting a separate pada [optionally become a bahuvrīhi].

We can define a dvandva quite simply:

• चार्थे द्वन्द्वः। २.२.२९
  cārthe dvandvaḥ (2.2.29)
  ca-arthe dvandvaḥ
  [Many related padas] (connected) in the sense of “and” [optionally become a dvandva].