Solidario, according to the RAE, means Adherido o asociado a la causa, empresa u opinión de alguien. Empresa?! Leave it to the RAE. I like the Vox definition better: adj. Que muestra solidaridad.
It turns out that the word solidary does technically exist in English, though it is not commonly used. The OED defines it as (adjective (of a group or community) characterized by solidarity or coincidence of interests). Others, like wiktionary, define it simply as having shared interests - which gets to whether you see solidarity as something that can happen across difference or not. It also seems that solidary is mostly used as legal terminology, as in solidary obligations. At any rate, it was a very solidary strike sounds odd to me and I have my doubts as to how easily understood it would be.
I like solidarious better than the Sp>Eng options offered by Collins for solidario listed below:
solidario
adj
1 (=humanitario) caring
Luis es muy solidario Luis is a very caring person
vivimos en un mundo poco solidario we live in an uncaring world, we live in a world where it's every man for himself
un acto solidario an act of solidarity
→ solidario con algo/algn
se ha mostrado muy solidario con nuestra causa he has been very sympathetic to our cause, he has shown a lot of solidarity with our cause
hacerse solidario con algo/algn to declare one's solidarity with sth/sb
→ solidario de algo frm hacerse solidario de una opinión to echo an opinion
Luis es muy solidario Luis is a very caring person
vivimos en un mundo poco solidario we live in an uncaring world, we live in a world where it's every man for himself
un acto solidario an act of solidarity
→ solidario con algo/algn
se ha mostrado muy solidario con nuestra causa he has been very sympathetic to our cause, he has shown a lot of solidarity with our cause
hacerse solidario con algo/algn to declare one's solidarity with sth/sb
→ solidario de algo frm hacerse solidario de una opinión to echo an opinion
2 (Jur)
[compromiso] mutually binding, shared in common
[participación] joint, common
[firmante, participante] jointly liable
responsabilidad solidaria joint liability
[compromiso] mutually binding, shared in common
[participación] joint, common
[firmante, participante] jointly liable
responsabilidad solidaria joint liability