extra duty allowance vs special duty allowance

extra duty allowance and special duty allowance both are nouns.

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

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

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

Other synonyms of extra duty allowance include extraneous duty allowance.

extra duty allowance (noun)	special 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.