regular vs first-string

regular is a noun but first-string is not a noun.

Word	Noun	Adjective	Verb	Adverb
regular	Yes	Yes	No	No
first-string	No	Yes	No	No

regular (noun)	first-string (noun)
a garment size for persons of average height and weight
a regular patron
a dependable follower (especially in party politics)
a soldier in the regular army

regular (adjective)	first-string (adjective)
in accordance with fixed order or procedure or principle	being a regular member of a team
(of solids) having clear dimensions that can be measured; volume can be determined with a suitable geometric formula	of members of a team; not substitutes
(used of the military) belonging to or engaged in by legitimate army forces
not constipated
relating to a person who does something regularly
officially full-time
not deviating from what is normal
regularly scheduled for fixed times
conforming to a standard or pattern
occurring at fixed intervals
symmetrically arranged
often used as intensifiers
in accord with regular practice or procedure