join vs solder

join and solder both are nouns.

Word	Noun	Adjective	Verb	Adverb
join	Yes	No	Yes	No
solder	Yes	No	Yes	No

As verbs, solder is a hyponym of join; that is, solder is a word with a more specific, narrower meaning than join:

join (noun)	solder (noun)
a set containing all and only the members of two or more given sets	an alloy (usually of lead and tin) used when melted to join two metal surfaces
the shape or manner in which things come together and a connection is made

join (verb)	solder (verb)
make contact or come together	join or fuse with solder
cause to become joined or linked
become part of; become a member of a group or organization
come into the company of
be or become joined or united or linked