Wiktionary:Referencing dictionaries

Dictionaries are not primary sources, and cannot be used for attestation.

Dictionaries are, however, useful references for substantiation (as per ELE).

Use and misuse of referencing dictionaries

 * Referring to other dictionaries is fine to clarify (or even correct) a definition.
 * But other dictionaries are not valid citations for a request for verification.

Appearance in a dictionary does not satisfy the Criteria For Inclusion (CFI), and a dictionary reference does not satisfy a Request For Verification (RFV).

User-contributed dictionaries
User-contributed dictionaries are problematic because they are prone to nonce words and protologisms, but can provide color.

Referencing them as a main citation can be an indication that a word does not meet CFI.