special duty allowance vs extra duty allowance

special duty allowance and extra duty allowance both are nouns.

Word	Noun	Adjective	Verb	Adverb
special duty allowance	Yes	No	No	No
extra duty allowance	Yes	No	No	No

As nouns, special duty allowance and extra duty allowance are synonyms defined as:

special duty allowance and extra duty allowance: an allowance payable to employees who are given special assignments or perform additional duties.

Other synonyms of special duty allowance include extraneous duty allowance.

special duty allowance (noun)	extra duty allowance (noun)
an allowance payable to employees who are given special assignments or perform additional duties.	an allowance payable to employees who are given special assignments or perform additional duties.